OMAP: DSS2: OMAPFB: Convert the memory region locking to rwsem

R/W semaphore is a good fit for the memory region locking pattern.
So use it.

Signed-off-by: Ville Syrjälä <ville.syrjala@nokia.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>
diff --git a/drivers/video/omap2/omapfb/omapfb-main.c b/drivers/video/omap2/omapfb/omapfb-main.c
index eb4338b..a3f72ba 100644
--- a/drivers/video/omap2/omapfb/omapfb-main.c
+++ b/drivers/video/omap2/omapfb/omapfb-main.c
@@ -1930,7 +1930,7 @@
 
 		ofbi->region = &fbdev->regions[i];
 		ofbi->region->id = i;
-		mutex_init(&ofbi->region->mtx);
+		init_rwsem(&ofbi->region->lock);
 
 		/* assign these early, so that fb alloc can use them */
 		ofbi->rotation_type = def_vrfb ? OMAP_DSS_ROT_VRFB :