chore(clippy): fix unneeded late initialization

The re-formatting made clippy aware of this unneeded late
initialization. Let's fix it.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

src/vmm/src/builder.rs

@@ -655,17 +655,16 @@ where
 {
     use self::StartMicrovmError::{InitrdLoad, InitrdRead};
 
-    let size: usize;
     // Get the image size
-    match image.seek(SeekFrom::End(0)) {
+    let size = match image.seek(SeekFrom::End(0)) {
         Err(err) => return Err(InitrdRead(err)),
         Ok(0) => {
             return Err(InitrdRead(io::Error::new(
                 io::ErrorKind::InvalidData,
                 "Initrd image seek returned a size of zero",
             )));
         }
-        Ok(s) => size = u64_to_usize(s),
+        Ok(s) => u64_to_usize(s),
     };
     // Go back to the image start
     image.seek(SeekFrom::Start(0)).map_err(InitrdRead)?;