soc/intel/broadwell/gma.c: Add missing `break` in switch

Otherwise, the `GT_CDCLK_675` case falls through and exits early.

Change-Id: Icb979f8a980e1a1e1c712c5d9bc8d94c90376b7f
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50141
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/soc/intel/broadwell/gma.c

@@ -476,6 +476,7 @@ static void igd_cdclk_init(struct device *dev, const int is_broadwell)
 		dpdiv = 338;
 		reg_em4 = 8;
 		reg_em5 = 225;
+		break;
 	default:
 		return;
 	}