FROMLIST: msm: mdss: handle synchronization issues during DSI debugfs read/write

Handle race condition during read/write operations to DSI debugfs nodes
related to DSI panel ON/OFF commands.

Change-Id: I29c4ad74bf21d4cb5362565e902a682fe7263147
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>

Bug: 33752702
(am from https://source.codeaurora.org/quic/la/kernel/msm-3.18/commit/?id=67dfd3a65336e0b3f55ee83d6312321dc5f2a6f9

)
Signed-off-by: Yueyao Zhu <yueyao@google.com>