tests/mpu_stack_guard: fix alignment issue

tests/mpu_stack_guard/Makefile

@@ -18,13 +18,13 @@ BOARD_WHITELIST += mbed_lpc1768     # cortex-m3
 BOARD_WHITELIST += msbiot           # cortex-m4f
 BOARD_WHITELIST += mulle            # cortex-m4
 BOARD_WHITELIST += nrf52dk          # cortex-m4f
-BOARD_WHITELIST += nucleo-f103rb      # cortex-m3
+BOARD_WHITELIST += nucleo-f103rb    # cortex-m3
 BOARD_WHITELIST += nucleo-f207zg    # cortex-m3
-BOARD_WHITELIST += nucleo-f303re      # cortex-m4f
-BOARD_WHITELIST += nucleo-f334r8      # cortex-m4f
-BOARD_WHITELIST += nucleo-f401re      # cortex-m4f
-BOARD_WHITELIST += nucleo-f446re      # cortex-m4f
-BOARD_WHITELIST += nucleo-l152re      # cortex-m3
+BOARD_WHITELIST += nucleo-f303re    # cortex-m4f
+BOARD_WHITELIST += nucleo-f334r8    # cortex-m4f
+BOARD_WHITELIST += nucleo-f401re    # cortex-m4f
+BOARD_WHITELIST += nucleo-f446re    # cortex-m4f
+BOARD_WHITELIST += nucleo-l152re    # cortex-m3
 BOARD_WHITELIST += openmote-cc2538  # cortex-m3
 BOARD_WHITELIST += pba-d-01-kw2x    # cortex-m4
 BOARD_WHITELIST += remote           # cortex-m3