msm: mdss: dp: avoid aux transactions if dp cable is disconnected

There might be cases where DP cable can be disconnected while
read/write aux transactions are in progress. Avoid retrying
aux transactions if DP cable is disconnected.

Change-Id: Ie6f884c047c6ef3a1584160820e6d41ec0b1e01b
Signed-off-by: Narender Ankam <nankam@codeaurora.org>