gpio: cdev: fix a NULL-pointer dereference with DEBUG enabled

We are actually passing the gc pointer to chip_dbg() so we have to
srcu_dereference() it.

Fixes: 8574b5b4

 ("gpio: cdev: use correct pointer accessors with SRCU")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Closes: https://lore.kernel.org/lkml/179caa10-5f86-4707-8bb0-fe1b316326d6@samsung.com/


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>