fix test compilation for STM32L
fix test compilation for STM32L

There is no host command yet and the "hello" test is not using it.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BUG=None
TEST=make tests BOARD=discovery && make tests BOARD=link

Change-Id: Ib7f49f8e38270a8c537e352396b1966abc801511

coreboot/chrome-ec,alterapraxisptyltd/chromium-ec,thehobn/ec,md5555/ec,fourier49/BZ_DEV_EC,alterapraxisptyltd/chromium-ec,fourier49/BIZ_EC,gelraen/cros-ec,longsleep/ec,coreboot/chrome-ec,alterapraxisptyltd/chromium-ec,thehobn/ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,gelraen/cros-ec,gelraen/cros-ec,coreboot/chrome-ec,md5555/ec,mtk09422/chromiumos-platform-ec,longsleep/ec,mtk09422/chromiumos-platform-ec,longsleep/ec,fourier49/BIZ_EC,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,mtk09422/chromiumos-platform-ec,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,coreboot/chrome-ec,gelraen/cros-ec,mtk09422/chromiumos-platform-ec,alterapraxisptyltd/chromium-ec,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,thehobn/ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,longsleep/ec,fourier49/BIZ_EC,thehobn/ec,eatbyte/chromium-ec