msm: sde: rotator: release the second fence reference

rotator driver marks the fence to null after passing
it to client. This is invalid starting from kernel
rev 4.9 because it uses the dma fence APIs. These
APIs takes two reference while creating the fence
and it is client's responsibility to release the
first fence.

Change-Id: I2c1d175144df5c5a75fb060a61ac1c23bdd34976
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>