Ryu: increase HOST_CMD stack size
Ryu: increase HOST_CMD stack size

Hit overflow while sending autocalibrate command.

At rest, we were already close to the limit:
   7   HOSTCMD          00000000    0.104035  472/488
Increase to 640 bytes.

BUG=chrome-os-partner:44381
BRANCH=ryu
TEST=Check auto calibrate works.

Change-Id: Ife014baf4316cdca952104c5158f38cd106e023f
Signed-off-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/295590
Reviewed-by: Sheng-liang Song <20a24593f82e573953076a0eeaf8f3cfb817a534@chromium.org>

coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec