pd: Add error handling for pd_send_request_msg()
pd: Add error handling for pd_send_request_msg()

If we have already completed negotiation as a sink and
pd_send_request_msg() fails, issue a soft reset so we don't remain
indefinitely at our previously negotiated voltage.

BUG=chrome-os-partner:50346
BRANCH=glados
TEST=Manual on chell. Attach zinger to port 1, then attach zinger to
port 2. Verify that port 1 negotiated to 20V. Detach port 1 and verify
port 2 successfully negotiates to 20V and begins charging.

Change-Id: I4f8ff9a1e3ef49858f6ae5c3ccb5b5d4d847e2d1
Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/332642
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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