drm/tilcdc: Clear bits of register we're going to set.

Bits weren't cleared so resolution changes didn't work.

Signed-off-by: Pantelis Antoniou <[e-mail]>
Signed-off-by: Darren Etheridge <[e-mail]>
Acked-by: Rob Clark <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/tilcdc/tilcdc_crtc.c

···
 	 * a value of 0 as 1
 	 */
 	if (priv->rev == 2) {
+		/* clear bits we're going to set */
+		reg &= ~0x78000033;
 		reg |= ((hfp-1) & 0x300) >> 8;
 		reg |= ((hbp-1) & 0x300) >> 4;
 		reg |= ((hsw-1) & 0x3c0) << 21;