[media] rcar-vin: remove subdevice matching from bind and unbind callbacks

There is only one subdevice registered with the async framework so there
is no need for the driver to check which subdevice is bound or unbound.
Remove these checks since the async framework preforms this.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
[hans.verkuil@cisco.com: fix typo: surce -> source]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>