gpio: gpiolib: remove shadowed variable

After refactoring, we had two variables for the same thing. Remove the
second declaration, one is enough here. Found by cppcheck.

drivers/gpio/gpiolib.c:2551:17: warning: Local variable 'ret' shadows outer variable [shadowVariable]

Fixes: d377f56f ("gpio: gpiolib: Normalize return code variable name")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>