qcacmn: Decrement peer ref count on rx hw stats req failure

Peer ref count incremented in dp_request_rx_hw_stats
is not decremented back in case of error scenarios
resulting in possible ref leak and failure in peer
deletion.

Fix is to invoke dp_peer_unref_delete for error
scenarios in dp_request_rx_hw_stats error.

Change-Id: I81ecf60a97ff5c804445fd713ed779c478df8521
CRs-Fixed: 2706596