SAM E54 Xplained devkit hardfaults at start with -O2

I don't know why, but other samd5x are using -Os too, see the block above.

Closes: #7277

Author: jepler

ports/atmel-samd/Makefile

@@ -79,7 +79,7 @@ endif
 
 ifeq ($(CHIP_FAMILY), same54)
 PERIPHERALS_CHIP_FAMILY=sam_d5x_e5x
-OPTIMIZATION_FLAGS ?= -O2
+OPTIMIZATION_FLAGS ?= -Os
 # TinyUSB defines
 CFLAGS += -DCFG_TUSB_MCU=OPT_MCU_SAME5X -DCFG_TUD_MIDI_RX_BUFSIZE=128 -DCFG_TUD_CDC_RX_BUFSIZE=256 -DCFG_TUD_MIDI_TX_BUFSIZE=128 -DCFG_TUD_CDC_TX_BUFSIZE=256 -DCFG_TUD_MSC_BUFSIZE=1024
 endif