[media] coda: remove context debugfs entry last

Do not remove the per-context debugfs directory before the
per-buffer debugfs entries contained therein.

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