gpio: xgs-iproc: remove __exit annotation for iproc_gpio_remove

When built into the kernel, the driver causes a link problem:

`iproc_gpio_remove' referenced in section `.data' of drivers/gpio/gpio-xgs-iproc.o: defined in discarded section `.exit.text' of drivers/gpio/gpio-xgs-iproc.o

Remove the incorrect annotation.

Fixes: 6a41b6c5 ("gpio: Add xgs-iproc driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>