drivers/pps/clients/pps-gpio.c: remove unnecessary platform_set_drvdata()

The driver core clears the driver data to NULL after device_release or on
probe failure.  Thus, it is not needed to manually clear the device driver
data to NULL.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Rodolfo Giometti <giometti@enneenne.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>