msm: mdss: Ensure pipe are unstaged before destroy

There are corner cases when pipes are still staged after
recovery sequence is over in overlay cleanup. Due to this
when destroying pipe, if pipe fetch halt tries to halt
the pipe, kernel bug happens and system gets crashed.
Hence, ensure pipes are unstaged before destroy.

Change-Id: If13ca0fce35656ecbc8f3c98e3017ac981dede06
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>