OMAP: DSS2: OMAPFB: fix omapfb_free_fbmem()

Fixes bug causing VRFB memory area to be released twice.

Signed-off-by: Tomi Valkeinen <[e-mail]>
Reported-by: Eino-Ville Talvala <[e-mail]>

drivers/video/omap2/omapfb/omapfb-main.c

···
 		if (rg->vrfb.vaddr[0]) {
 			iounmap(rg->vrfb.vaddr[0]);
 			omap_vrfb_release_ctx(&rg->vrfb);
+			rg->vrfb.vaddr[0] = NULL;
 		}
 	}