gpio: exar: remove unneeded platform_set_drvdata() call

The platform_set_drvdata() was needed when the driver had an explicit
remove function.
That function got removed a while back, so we don't need to keep a pointer
(on 'dev->driver_data') for the private data of the driver anymore.

Reviewed-by: Alexandru Ardelean <alex@shruggie.ro>
Signed-off-by: Andrei Coardos <aboutphysycs@gmail.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>