msm: mdss: fix autorefresh during kickoff

When autorefresh is enabled, any kickoff that
gets processed needs to wait to make sure the
transfer is on-going before continuing
the commit; current driver only waits for
autorefresh interrupt but this doesn't
guarantee that transfer is already on-going.
This change waits for the write pointer,
to make sure a transfer is on-going.

Change-Id: I247b3aad8f2f6ea8954d54f34492e293f80f99d4
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>