[media] coda: do not allocate maximum number of framebuffers for encoder

The encoder only ever needs two buffers, but we'll have to increase
CODA_MAX_FRAMEBUFFERS for the decoder.

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>