[media] omap3isp: ispqueue: Fix uninitialized variable compiler warnings

drivers/media/platform/omap3isp/ispqueue.c:399:18: warning: 'pa' may be
used uninitialized in this function [-Wuninitialized]
This is a false positive but the compiler has no way to know about it,
so initialize the variable to 0.
drivers/media/platform/omap3isp/ispqueue.c:445:6: warning:
'vm_page_prot' may be used uninitialized in this function
[-Wuninitialized]
This is a false positive and the compiler should know better. Use
uninitialized_var().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>