qcacmn: check hal_ring pointer before servicing the ring

Do null check before servicing the ring. When dp_service_srngs()
is common API which gets called when interrupt gets fired for
any ring. Within this API, driver goes one by one to each ring
and service the rings as it is not obvious from interrupt line that
which particular service ring needs to be served.

So race happens when rings are getting initialized and packet has been
arrived to one of the rings. Due to dp_service_srngs() API's
implementation, driver goes to one by one each ring without checking
if all rings are initialized.

CRs-Fixed: 2310496
Change-Id: I3c8f668756c8d266abe082e8473d54cb4df9065e

hal/wifi3.0/hal_api.h

@@ -398,6 +398,11 @@ static inline int hal_srng_access_start(void *hal_soc, void *hal_ring)
 {
 	struct hal_srng *srng = (struct hal_srng *)hal_ring;
 
+	if (qdf_unlikely(!hal_ring)) {
+		qdf_print("Error: Invalid hal_ring\n");
+		return -EINVAL;
+	}
+
 	SRNG_LOCK(&(srng->lock));
 
 	return hal_srng_access_start_unlocked(hal_soc, hal_ring);
@@ -801,6 +806,11 @@ static inline void hal_srng_access_end(void *hal_soc, void *hal_ring)
 {
 	struct hal_srng *srng = (struct hal_srng *)hal_ring;
 
+	if (qdf_unlikely(!hal_ring)) {
+		qdf_print("Error: Invalid hal_ring\n");
+		return;
+	}
+
 	hal_srng_access_end_unlocked(hal_soc, hal_ring);
 	SRNG_UNLOCK(&(srng->lock));
 }