gpio: mpsse: Check for error code from devm_mutex_init() call

gpio: mpsse: 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: c46a74ff05c0 ("gpio: add support for FTDI's MPSSE as GPIO")
Reviewed-by: Mary Strodl <mstrodl@csh.rit.edu>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20241030174132.2113286-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>