leds: st1202: Check for error code from devm_mutex_init() call

leds: st1202: Check for error code from devm_mutex_init() call

Even if it's not critical, the avoidance of checking the error code
from devm_mutex_init() call today diminishes the point of using devm
variant of it. Tomorrow it may even leak something. Add the missed
check.

Fixes: 259230378c65 ("leds: Add LED1202 I2C driver")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20250204-must_check-devm_mutex_init-v2-1-7b6271c4b7e6@weissschuh.net
Signed-off-by: Lee Jones <lee@kernel.org>