drm/msm/dp: fix command data for link polling requests

Fix the command data that is sent to the transport layer for link
polling requests by updating the buffer pointer to the request
buffer pointer from the HDCP library. This ensures that the
transport layer has a valid buffer pointer to use for messages
received from the sink. Furthermore, update the error messages in
the transport layer to correctly reflect the status of sent
messages.

Change-Id: Idc6124b635509547b7f4dca10ae0a895900e576d
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>