msm: mdss: DSI mode switch send dcs cmd with CMD_REQ

Regression in change I532587eaa763499c9d51909937339093cd74a8cf.
During DSI mode change we need to send dsc command with
CMD_REQ_COMMIT flag.

Change-Id: Ibc970c70c974cb020c05780f45341a9a99eb6e30
Signed-off-by: Terence Hampson <thampson@codeaurora.org>