Remove unnecessary qualification from size_of

Closes #12339

src/io.rs

@@ -420,8 +420,7 @@ pub fn read_once(fd: RawFd, buffer: &mut MutexGuard<'_, SeparatedBuffer>) -> isi
 
         // We want to swallow EINTR only; in particular EAGAIN needs to be returned back to the caller.
         let amt = loop {
-            let amt =
-                unsafe { libc::read(fd, bytes.as_mut_ptr().cast(), std::mem::size_of_val(&bytes)) };
+            let amt = unsafe { libc::read(fd, bytes.as_mut_ptr().cast(), size_of_val(&bytes)) };
             if amt < 0 && errno::errno().0 == EINTR {
                 continue;
             }