[media] gspca_pac7302: use registers 0x01 and 0x03 for red and blue balance controls

Currently used registers 0xc5 and 0xc7 provide only a very coarse
adjustment possibility within a very small value range (0-3).
With registers 0x01 and 0x03, a fine grained adjustment with
255 steps is possible. This is also what the Windows driver does.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>