disp: msm: dsi: Set the panel test gpio to input

This GPIO is a input signal, so need to set it
to input mode, or it will lead leakage in RBC.
This change is only to fix the power issue.

Change-Id: I87716f646c75dac2f1350a2ea55188829a4ccc9e
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>