[media] coda: coda-bit: Include "<linux/slab.h>"

coda-bit uses kmalloc/kfree functions, so the slab header needs to be included
in order to fix the following build errors:

drivers/media/platform/coda/coda-bit.c: In function 'coda_fill_bitstream':
drivers/media/platform/coda/coda-bit.c:231:4: error: implicit declaration of function 'kmalloc' [-Werror=implicit-function-declaration]
drivers/media/platform/coda/coda-bit.c: In function 'coda_alloc_framebuffers':
drivers/media/platform/coda/coda-bit.c:312:3: error: implicit declaration of function 'kfree' [-Werror=implicit-function-declaration]

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>