qcacmn: Add NULL check before unmapping desc

Add NULL check before unmapping desc

Change-Id: I633568f66dec04a5591a0161fce04c9392542e57
CRs-Fixed: 3481046

dp/wifi3.0/dp_tx.c

@@ -2125,8 +2125,10 @@ void dp_tx_nbuf_unmap(struct dp_soc *soc,
 static inline
 void dp_tx_enh_unmap(struct dp_soc *soc, struct dp_tx_desc_s *desc)
 {
-	dp_tx_nbuf_unmap(soc, desc);
-	desc->flags |= DP_TX_DESC_FLAG_UNMAP_DONE;
+	if (qdf_likely(!(desc->flags & DP_TX_DESC_FLAG_UNMAP_DONE))) {
+		dp_tx_nbuf_unmap(soc, desc);
+		desc->flags |= DP_TX_DESC_FLAG_UNMAP_DONE;
+	}
 }
 
 static inline void dp_tx_unmap(struct dp_soc *soc, struct dp_tx_desc_s *desc)