gpio: bcm-kona: remove unneeded platform_set_drvdata() call

The platform_set_drvdata() call was never used, ever since the driver was
originally added.
It looks like this copy+paste left-over. Possibly the author copied from a
driver that had this line, but also had a remove hook.

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