[media] v4l: omap3isp: use vb2_buffer_state enum for vb2 buffer state

use the vb2_buffer_state enum for assigning the state
of the vb2 buffer, along side making isp_pipeline_state
state variable local to the block.
This fixes the following sparse warning as well:
drivers/media/platform/omap3isp/ispvideo.c:497:35: warning: mixing different enum types
drivers/media/platform/omap3isp/ispvideo.c:497:35:     int enum isp_pipeline_state  versus
drivers/media/platform/omap3isp/ispvideo.c:497:35:     int enum vb2_buffer_state

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>