armv7m: mpu_config add missing break

For DEVICE_NON_SHARED the newly assigned value of attr
is overwritten due to a missing break.

The problem was indicated by cppcheck.
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>

arch/arm/cpu/armv7m/mpu.c

@@ -68,6 +68,7 @@ void mpu_config(struct mpu_region_config *reg_config)
 		break;
 	case DEVICE_NON_SHARED:
 		attr = (2 << TEX_SHIFT) | BUFFERABLE;
+		break;
 	default:
 		attr = 0; /* strongly ordered */
 		break;