media: v4l2-mediabus: use BIT() macro for flags

Instead of using (1 << n) for bits, use the BIT() macro,
as it makes a difference from documentation point of view.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>