[media] mt9m001: avoid calling mt9m001_find_datafmt() twice

Simplify mt9m001_s_fmt and mt9m001_set_fmt.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>