[media] si4713: switch reset gpio to devm_gpiod API

This updates the driver to use the managed gpiod interface
instead of the unmanged old GPIO API. This is a preperation
for the introduction of device tree support.

Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
[hans.verkuil@cisco.com: fixed trivial compiler warning]

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>