msm: synx: fence callback fixes

Callbacks with the backing dma fences are not registered
for composite (merged) synx objects.
Hence added check to exclude dma fence removal for the
merged objects during cleanup.
Also, the check for the synx object status is moved prior
to dma fence callback removal as any attempts to re-signal
a signaled object does not attempt to remove dma fence
callback again.

Change-Id: Idbbdf1d813ed1099d35044d2e454d60017fe172a
Signed-off-by: Sumukh Hallymysore Ravindra <shallymy@codeaurora.org>