drm/msm/sde: don't duplicate input fence pointer with state

Avoid duplicating the input fence structure within the plane
driver's duplicate state callback. The user context is not
always available at this point and the pointer can't be
safely copied without taking an extra reference to it.

Change-Id: I0aeb4f83b871e4c9add95113ffc80f10b56f51a6
Signed-off-by: Clarence Ip <cip@codeaurora.org>