usb-pd: Clear active contract bit before browning out system
usb-pd: Clear active contract bit before browning out system

In the case where we are resetting Vbus and it is our only power source,
then we will brown out before we set the active port to 0.

BRANCH=none
BUG=none
TEST=Did a cold reset on grunt with no battery power. System booted as
normal.

Change-Id: I3823af6b0475e4cf8abbe12dd8ae4ceef26d1eab
Signed-off-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/911613
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Reviewed-by: Edward Hill <db1406b34e091703092b6b136bdfeb2c8125fc0e@chromium.org>

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