[media] gspca_pac7302: add sharpness control

The Windows driver uses page 0 register 0xb6 for sharpness adjustment.

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>