power/mt8192: remove unused variable
power/mt8192: remove unused variable

BUG=none
TEST=makeall
BRANCH=none

Signed-off-by: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@google.com>
Change-Id: If1199ed3ad87867c7d6ace54c0865369e6cf7638
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3275003
Tested-by: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>
Auto-Submit: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>
Reviewed-by: Eric Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@google.com>
Commit-Queue: Eric Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@google.com>

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