media: saa7146: make use of i2c_8bit_addr_from_msg

Because it looks neater.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>