[media] media: s5p_mfc: Release ctx->ctx if failed to allocate ctx->shm

ctx->ctx should be released if the following allocation for ctx->shm
gets failed.

Signed-off-by: Zhaowei Yuan <zhaowei.yuan@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>