drm/msm/dp: clear CP_IRQ bit during hdcp2p2 authentication

Though CP_IRQ bit is being cleared during HDCP1.4 authentication,
it is not being cleared during HDCP2.2 authentication.
This change now clears CP_IRQ bit after processing cp_irq handler
during HDCP2.2 authentication.

Change-Id: Ice165322d4fc5bfa5c43d62e33d2eab5452d9a29
Signed-off-by: Narender Ankam <nankam@codeaurora.org>