zephyr: spinmutex: Fix Debug message type

Print the type of this item specifically as SpinMutex instead of just
Mutex, so that it if is used in debug messages, it will be helpful (and
correct).

Signed-off-by: David Brown <[email protected]>

zephyr/src/sync/spinmutex.rs

@@ -55,7 +55,7 @@ unsafe impl<T: ?Sized + Send> Sync for SpinMutex<T> {}
 
 impl<T> fmt::Debug for SpinMutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "Mutex {:?}", self.inner)
+        write!(f, "SpinMutex {:?}", self.inner)
     }
 }