V4L/DVB (10673): mt9t031: fix gain and hflip controls, register update, and scaling

Multiple fixes:
1. allow register update by setting the Output Control register to 2 and not 3
2. fix scaling factor calculations
3. recover lost HFLIP control
4. fix Global Gain calculation

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>