servo_micro: increase stack size
servo_micro: increase stack size

This resolves occasional stack overflows.

BRANCH=none
BUG=b:79684405
TEST=No longer getting stack overflows.

Change-Id: Ib9188b4e4e0c5c87f34c87f490ae8bc26e34e041
Signed-off-by: Matthew Blecker <d18f4466f2802f9c78c5c14a42b8c21fdbfabfcd@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1152564
Reviewed-by: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec