Input: adp5588-keys - use guard notation when acquiring mutexes

This makes the code more compact and error handling more robust.

Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://lore.kernel.org/r/20240826-adp5588_gpio_support-v11-1-3e5ac2bd31b7@analog.com


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