msm: mdss: fix the use after free problem in rotator ioctl

Currently the fence fd is installed too early. This can cause a
use after free problem if the fence fd is closed in some other thread.
This change will install the fence fd where it is required and
eliminates the problem.

Change-Id: I5cf585ea87ef75fccae06da6cb5a6c16fc74eff3
Signed-off-by: Harsh Sahu <hsahu@codeaurora.org>