servo_micro: increase SPI clock
servo_micro: increase SPI clock

While SPI routing on servo is not great, this is still fine
and asn't as painfully slow.

BUG=chromium:571477
TEST=flash some firmware
BRANCH=None

Change-Id: I26d67ed6cd1ba62a892388e96a21acc708265fc4
Signed-off-by: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/366670
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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