[media] coda: add coda_bit_stream_set_flag helper

This adds a helper function to consolidate three occurences where
the bitstream parameter stream end flag is set during operation.

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>