[media] coda: remove BUG() in get_q_data

This allows us to get rid of the now superfluous v4l2_m2m_get_vq check
in G_FMT. Also, we can use this to check the buffer type in G_SELECTION
later.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>