stm32f0: Change idle task warning printf to save stack space
stm32f0: Change idle task warning printf to save stack space

Change the idle task overslept warning printf to save stack space.
The current warning uses CPRINTF which adds too much to the stack
and overflows the idle stack.

BUG=chrome-os-partner:33138, chrome-os-partner:36636
BRANCH=samus
TEST=comment out the if (margin_us < 0) check and always print
warning message. Without this CL stack overflows. With this CL,
stack does not overflow and gets to 168/256, which is plenty of
headroom considering the task doesn't do much.

Change-Id: I19a8336b8584d2a1342e7b9290aad471d326a060
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/250300
Reviewed-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

coreboot/chrome-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,md5555/ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,fourier49/BIZ_EC,md5555/ec,fourier49/BIZ_EC,fourier49/BIZ_EC,eatbyte/chromium-ec,md5555/ec,md5555/ec,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec