msm: kgsl: Properly remove ref count on gpuobj_sync failure

The user can pass bad data into kgsl_ioctl_gpuobj_sync(). If
_copy_from_user() fails do to bad data, undo any current
references taken through this ioctl call.

Change-Id: I56195520b9dadba20ee419658fc2cbb282b8449c
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>