blackfin video driver: fix bug when opening/reading/mmaping BF54x and BF52x framebuffer simultaneously

http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=3974

opening/reading/mmaping BF54x and BF52x framebuffer simultaneously triggers
BUG: failure at mm/nommu.c:470/add_nommu_vma() Add VM_SHARED to the default
vm_flags

Signed-off-by: Michael Hennerich <[e-mail]>
Signed-off-by: Bryan Wu <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: "Antonino A. Daplas" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/video/bf54x-lq043fb.c

···
 	 *   Other flags can be set, and are documented in
 	 *   include/linux/mm.h
 	 */
-	vma->vm_flags |= VM_MAYSHARE;
+	vma->vm_flags |=  VM_MAYSHARE | VM_SHARED;
 
 	return 0;
 }

drivers/video/bfin-t350mcqb-fb.c

···
 	 *   Other flags can be set, and are documented in
 	 *   include/linux/mm.h
 	 */
-	vma->vm_flags |= VM_MAYSHARE;
+	vma->vm_flags |= VM_MAYSHARE | VM_SHARED;
 
 	return 0;
 }