Input: pxrc - simplify mutex handling with guard macro

Use the guard(mutex) macro for handle mutex lock/unlocks.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Link: https://lore.kernel.org/r/20231202-pxrc-guard-v3-1-2ca8bc8cf689@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>