leds: leds-gpio: Pass on error codes unmodified

Instead of overriding error codes, pass them on unmodified. This
way a EPROBE_DEFER is correctly passed to the driver core. This results
in the LED driver correctly requesting probe deferral in cases the GPIO
controller is not yet available.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Reported-and-tested-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Bryan Wu <cooloney@gmail.com>