msm: camera: sync: Allow drivers to register cb for the same fence id

In batch mode, to get better result, LRME HW needs to process the first
and the last frame of the first batch as REF and TAR. Since those two
frames share the same fence id, LRME needs to be able to register the
callback with this fence twice. Without this change, the second callback
would be rejected, and hence the first config packet would fail.

Change-Id: Ib13cc284e7c41f5c411bbc5b4e94fe7fbd9b9c12
Signed-off-by: Junzhe Zou <jnzhezou@codeaurora.org>