[media] media: i2c: ths7303: remove unnecessary function ths7303_setup()

the ths7303_setup() was doing the same thing as ths7303_setval()
except that ths7303_setval() sets it to some particular mode.
This patch removes ths7303_setup() function and calls ths7303_setval()
in the probe setting the device to 480I_576I filter mode in the probe.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>