Replace the manual mutex lock/unlock pairs with guard() for code
simplification.
As replaced with the guard(mutex), no longer used snd_gf1_mem_lock()
is dropped, too.
Only code refactoring, and no behavior change.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250829145300.5460-8-tiwai@suse.de