V4L/DVB (6270): V4L: Honor dev->ctl_invert when setting up the decoder in saa7134

When user sets dev->ctl_invert, driver writes negative values to
SAA7134_DEC_LUMA_CONTRAST and SAA7134_DEC_CHROMA_SATURATION,
but general code that initializes decorder ignores that

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>