gpio: grgpio: Add NULL check in grgpio_probe

gpio: grgpio: Add NULL check in grgpio_probe

devm_kasprintf() can return a NULL pointer on failure,but this
returned value in grgpio_probe is not checked.
Add NULL check in grgpio_probe, to handle kernel NULL
pointer dereference error.

Cc: stable@vger.kernel.org
Fixes: 7eb6ce2f2723 ("gpio: Convert to using %pOF instead of full_name")
Signed-off-by: Charles Han <hanchunchao@inspur.com>
Link: https://lore.kernel.org/r/20241114091822.78199-1-hanchunchao@inspur.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>