[media] gspca_zc3xx: Fix JPEG quality setting code

[media] gspca_zc3xx: Fix JPEG quality setting code

The current code is using bits 0-1 of register 8 of the zc3xx controller
to set the JPEG quality, but the correct bits are bits 1-2. Bit 0 selects
between truncation or rounding in the quantization phase of the compression,
since rounding generally gives better results it should thus always be 1.

This patch also corrects the quality percentages which belong to the 4
different settings.

Last this patch removes the different reg 8 defaults depending on the sensor
type. Some of them where going for a default quality setting of 50%, which
generally is not necessary in any way and results in poor image quality.
75% is a good default to use for all scenarios.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>