media: platform: Use gpio_is_valid()

Replace the manual validity checks for the GPIO with the
gpio_is_valid().

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>