qcacmn: Handle the duplicate entries in reo exception ring

We have come across scenarios where rxdma is pushing
a certain entry more than once to the reo exception
ring. In this scenario, when we try to unmap a buffer,
it can lead to multiple unmap of the same buffer.

Handle this case, by skipping the process of this
duplicate entry, if alrady unmapped, and proceed to the
next entry.

Change-Id: Iae66f27e432f795ba4730911029fa1d63a75cb06
CRs-Fixed: 2739176