[media] V4L: soc-camera: (cosmetic) use a more explicit name for a host handler

Use "enum_framesizes" instead of "enum_fsizes" to more precisely follow
the name of the respective ioctl().

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Reviewed-by: Sergio Aguirre <sergio.a.aguirre@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>