mutex_lock() can sleep, don't call mutex_lock() while holding spin_lock.

Fixes: bc0ae0e7 ("gpio: add driver for Mellanox BlueField 2 GPIO controller")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: asmaa@mellanox.com
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>