[media] gspca: dubious one-bit signed bitfield

This patch changes some signed integers to unsigned because
they are not intended for negative values and sparse
is making noise about it.

Sparse gives eight of these errors:
drivers/media/usb/gspca/ov519.c:144:29: error: dubious one-bit signed bitfield

Signed-off-by: Emil Goode <emilgoode@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>