fix(test): move import to where its needed

The usesite of this import was behind a cfg, so some feature combos
printed a warning about unused imports.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/mmap/mod.rs

@@ -493,7 +493,6 @@ mod tests {
     use crate::GuestAddressSpace;
 
     use std::io::Write;
-    use std::mem;
     #[cfg(feature = "rawfd")]
     use std::{fs::File, path::Path};
     use vmm_sys_util::tempfile::TempFile;
@@ -942,7 +941,7 @@ mod tests {
                 format!("{:?}", gm.write_obj(val1, bad_addr2).err().unwrap()),
                 format!(
                     "PartialBuffer {{ expected: {:?}, completed: {:?} }}",
-                    mem::size_of::<u64>(),
+                    std::mem::size_of::<u64>(),
                     max_addr.checked_offset_from(bad_addr2).unwrap()
                 )
             );
@@ -991,6 +990,8 @@ mod tests {
     #[test]
     #[cfg(feature = "rawfd")]
     fn read_to_and_write_from_mem() {
+        use std::mem;
+
         let f = TempFile::new().unwrap().into_file();
         f.set_len(0x400).unwrap();