[media] V4L: soc-camera: fix compiler warnings on 64-bit platforms

On 64-bit platforms assigning a pointer to a 32-bit variable causes a
compiler warning and cannot actually work. Soc-camera currently doesn't
support any 64-bit systems, but such platforms can be added in the
and in any case compiler warnings should be avoided.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>