pd: pd_send_vdm function causes an assert when called from non pd task
pd: pd_send_vdm function causes an assert when called from non pd task

pd_send_vdm is an API function that can be called from any task but it
generates an assert if called outside the pd task.

BUG=b:140939776
BRANCH=none
TEST=manual

Change-Id: Id5c61542ba3b6422fb08dc8de88694b120fb9043
Signed-off-by: Sam Hurst <500b4cddcd66abe3fe333e92c4c95d7f41e62e4e@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1801854
Tested-by: Sam Hurst <500b4cddcd66abe3fe333e92c4c95d7f41e62e4e@google.com>
Reviewed-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Commit-Queue: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>

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