ix huge lookup array

Since V4L2_MBUS_FMT_* codes have become large and sparse, they cannot
be used as array indices anymore.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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