msm: mdss: avoid color fill call if flag is not set

Current code tries to force a color fill if it does not
find a buffer associated with the pipe, this is wrong
and causes underruns due misconfiguration in the pipe.
This fix modify this behavior to only do color fill
if it is requested through the flags.

Change-Id: I019da850a05a3c26f0a72626f1c442cfdac8733b
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>