V4L/DVB (13142): gspca_mr97310a: small tweak to CIF sensor type 1 exposure setting

The CIF sensor type 1 exposure setting got clamped at 300, as settings below
300 do not work well (and do work for the other sensors). This patch
scales the 0-4095 range to 300-4095 instead of ignoring changes between
300, avoiding have a part of the control range where nothing happens.

This is esp. important for software autogain as done by libv4l.

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