pd: fix duplicate PD receive event on combined TCPM/TCPC
pd: fix duplicate PD receive event on combined TCPM/TCPC

Fix duplicate PD RX event when using combined TCPM/TCPC. Problem
is that PD_EVENT_RX is already set in the phy layer in pd_rx_event
when CC edges are detected. Therefore, we shouldn't set it again
when the TCPC detects that receiving has started.

BUG=none
BRANCH=none
TEST=test on samus. without this change we occasionally get a
PD error and hard reset under certain timing circumstances due
to the repeated event. with this change, those errors go away.

Change-Id: If1034a549b75740f327e16810e81c9aa28d71b00
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/273418
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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