cellular: Fix CellularProxy.reset_modem() Powered state check

BUG=chromium:417105
TEST=network_3GSmokeTest

Change-Id: Ifc2b69f490ce33465b03da3e1a5c1741a7416968
Reviewed-on: https://chromium-review.googlesource.com/219634
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Thieu Le <thieule@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
2 files changed