drm/edid: don't return stack garbage from supports_rb

We need to initialize this to false, because the is_rb callback only
ever sets it to true.

Noticed while reading through the code.

Cc: stable@vger.kernel.org
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_edid.c

@@ -610,7 +610,7 @@ static bool
 drm_monitor_supports_rb(struct edid *edid)
 {
 	if (edid->revision >= 4) {
-		bool ret;
+		bool ret = false;
 		drm_for_each_detailed_block((u8 *)edid, is_rb, &ret);
 		return ret;
 	}