g: fix hwtimer event deadline
g: fix hwtimer event deadline

We were losing timer events because usecs_to_ticks(deadline) was
clipping the value when deadline was larger than 0x08888888 (deadline is
a timestamp rather than a delay).
The computation of the timer deadline has been modified to avoid the
clipping issue.

Signed-off-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

BRANCH=none
BUG=chrome-os-partner:34347
TEST=run on Cr50 with the watchdog activated and no longer see watchdog
warnings.
Run the "timer_calib" test and see that the 1s sleep is 1000038 us :
make BOARD=cr50 tests
fhl ../build/cr50/timer_calib/timer_calib.RO.hex

Change-Id: Id2200a89eb1b72099e536291af321609b24b4777
Reviewed-on: https://chromium-review.googlesource.com/233531
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Trybot-Ready: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Commit-Queue: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

md5555/ec,coreboot/chrome-ec,fourier49/BIZ_EC,coreboot/chrome-ec,md5555/ec,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,mtk09422/chromiumos-platform-ec,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,eatbyte/chromium-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,mtk09422/chromiumos-platform-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,fourier49/BZ_DEV_EC,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,md5555/ec,coreboot/chrome-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics