[qca-nss-dp] Add check for tpd before the usage

Add NULL check for the tpd pointer before using it.

Change-Id: I2f5d988a0c851b3a009f48a34c3bf0f69043d11c
Signed-off-by: Rakesh Nair <ranair@codeaurora.org>
diff --git a/edma.c b/edma.c
index 30644a8..0285de3 100644
--- a/edma.c
+++ b/edma.c
@@ -1490,7 +1490,8 @@
 			 */
 			edma_cinfo->edma_ethstats.tx_prec[precedence]++;
 			edma_cinfo->edma_ethstats.tx_ac[edma_dscp2ac_tbl[precedence]]++;
-			tpd->word3 |= precedence << EDMA_TPD_PRIO_SHIFT;
+			if (tpd)
+				tpd->word3 |= precedence << EDMA_TPD_PRIO_SHIFT;
 		}
 
 		/* If sysctl support for IAD stats are enabled */