binder: use guards for plain mutex- and spinlock-protected sections

binder: use guards for plain mutex- and spinlock-protected sections

Use 'guard(mutex)' and 'guard(spinlock)' for plain (i.e. non-scoped)
mutex- and spinlock-protected sections, respectively, thus making
locking a bit simpler. Briefly tested with 'stress-ng --binderfs'.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20250626073054.7706-2-dmantipov@yandex.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>