Add linux/sched.h because of missing declaration of TASK_NORMAL.

This patch fixes the following error:

drivers/media/video/omap24xxcam.c: In function
'omap24xxcam_vbq_complete':
drivers/media/video/omap24xxcam.c:415: error: 'TASK_NORMAL' undeclared
(first use in this function)
drivers/media/video/omap24xxcam.c:415: error: (Each undeclared
identifier is reported only once
drivers/media/video/omap24xxcam.c:415: error: for each function it
appears in.)
Signed-off-by: Thomas Weber <weber@corscience.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>