rustc: Fix mismatched_lifetime_syntaxes

Rust v1.89.0 is reporting rustc::mismatched_lifetime_syntaxes:

```console
warning: hiding a lifetime that's elided elsewhere is confusing
   --> src/devices/src/virtio/descriptor_utils.rs:499:13
    |
499 |     memory: &GuestMemoryMmap,
    |             ^^^^^^^^^^^^^^^^ the lifetime is elided here
...
504 | ) -> Result<DescriptorChain> {
    |             --------------- the same lifetime is hidden here
    |
    = help: the same lifetime is referred to in inconsistent ways, making the signature confusing
    = note: `#[warn(mismatched_lifetime_syntaxes)]` on by default
help: use `'_` for type paths
    |
504 | ) -> Result<DescriptorChain<'_>> {
    |                            ++++
```

fix as suggested by rustc to kill those warnings.

Signed-off-by: Ruoqing He <[email protected]>

Author: RuoqingHe

src/devices/src/virtio/descriptor_utils.rs

@@ -501,7 +501,7 @@ pub fn create_descriptor_chain(
     mut buffers_start_addr: GuestAddress,
     descriptors: Vec<(DescriptorType, u32)>,
     spaces_between_regions: u32,
-) -> Result<DescriptorChain> {
+) -> Result<DescriptorChain<'_>> {
     let descriptors_len = descriptors.len();
     for (index, (type_, size)) in descriptors.into_iter().enumerate() {
         let mut flags = 0;

src/devices/src/virtio/mmio.rs

@@ -195,7 +195,7 @@ impl MmioTransport {
         self.interrupt.event()
     }
 
-    pub fn locked_device(&self) -> MutexGuard<dyn VirtioDevice + 'static> {
+    pub fn locked_device(&self) -> MutexGuard<'_, dyn VirtioDevice + 'static> {
         self.device.lock().expect("Poisoned device lock")
     }
 

src/devices/src/virtio/queue.rs

@@ -225,7 +225,7 @@ impl<'a> DescriptorChain<'a> {
         desc_table: GuestAddress,
         queue_size: u16,
         index: u16,
-    ) -> Option<DescriptorChain> {
+    ) -> Option<DescriptorChain<'_>> {
         if index >= queue_size {
             return None;
         }

src/hvf/src/lib.rs

@@ -523,7 +523,7 @@ impl HvfVcpu<'_> {
         }
     }
 
-    fn handle_psci_request(&self) -> Result<VcpuExit, Error> {
+    fn handle_psci_request(&self) -> Result<VcpuExit<'_>, Error> {
         match self.read_reg(hv_reg_t_HV_REG_X0)? {
             0x8400_0000 /* QEMU_PSCI_0_2_FN_PSCI_VERSION */ => {
                 self.write_reg(hv_reg_t_HV_REG_X0, 2)?;
@@ -550,7 +550,7 @@ impl HvfVcpu<'_> {
         }
     }
 
-    pub fn run(&mut self, vcpu_list: Arc<dyn Vcpus>) -> Result<VcpuExit, Error> {
+    pub fn run(&mut self, vcpu_list: Arc<dyn Vcpus>) -> Result<VcpuExit<'_>, Error> {
         let pending_irq = vcpu_list.has_pending_irq(self.vcpuid);
 
         if let Some(mmio_read) = self.pending_mmio_read.take() {

src/krun_display/src/rust_to_c.rs

@@ -36,13 +36,13 @@ pub trait DisplayBackendBasicFramebuffer {
 }
 
 pub trait IntoDisplayBackend<T: Sync> {
-    fn into_display_backend(userdata: Option<&T>) -> DisplayBackend;
+    fn into_display_backend(userdata: Option<&T>) -> DisplayBackend<'_>;
 }
 
 impl<T: Sync, I: DisplayBackendBasicFramebuffer + DisplayBackendNew<T>> IntoDisplayBackend<T>
     for I
 {
-    fn into_display_backend(userdata: Option<&T>) -> DisplayBackend {
+    fn into_display_backend(userdata: Option<&T>) -> DisplayBackend<'_> {
         extern "C" fn create_fn<T: Sync, I: DisplayBackendNew<T>>(
             instance: *mut *mut c_void,
             userdata: *const c_void,