msm: mdss: Signal outstanding fences when panel is dead

When the panel is in dead state, we early return from
the commit. So, the fences wouldn't be signalled till
the next Blank call. Handling this case by signalling
the outstanding fences when panel is in dead state.

Change-Id: I48a5e04707e32de0d1cdccf0592c981e30b618fc
Signed-off-by: Krishna Chaitanya Devarakonda <kdevarak@codeaurora.org>