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: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/arch/arm/cpu/armv7m/mpu.c b/arch/arm/cpu/armv7m/mpu.c
index 31a243b..4622aa4 100644
--- a/arch/arm/cpu/armv7m/mpu.c
+++ b/arch/arm/cpu/armv7m/mpu.c
@@ -68,6 +68,7 @@
 		break;
 	case DEVICE_NON_SHARED:
 		attr = (2 << TEX_SHIFT) | BUFFERABLE;
+		break;
 	default:
 		attr = 0; /* strongly ordered */
 		break;