drm/msm/sde: release the fence refcount on signal

fence_init API initializes the fence refcount. It
should be released on fence signaled to avoid holding
refcount taken during fence_init and avoid memory leak.
The patch also removes the fence list handling from
release API. Such handling is not necessary because
fence_signal API removes the node from list and signal
it after.

Change-Id: I12e24d07970b2d2230d980e156fbea4a724434d0
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>