[media] [for,v3.14] sn9c102: fix build dependency

This driver should only build if MEDIA_USB_SUPPORT is set.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Jim Davis <jim.epost@gmail.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>