msm: mdss: acquire pipe before overlay start in pan display

acquire pipe before overlay start so that splash cleanup
can happen in overlay start.

Change-Id: I1ef3dbabf264925fee2eb903beed183eba335bb2
Signed-off-by: Kalyan Thota <kalyant@codeaurora.org>
Signed-off-by: Anusha Koduru <kanusha@codeaurora.org>