[media] si4713: fix Kconfig dependencies

The SI4713 select should be I2C_SI4713 and the USB driver needs to depend on
I2C as well.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Paul Bolle <pebolle@tiscali.nl>
Reported-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>