qcacmn: Fix build error when DISABLE_MON_CONFIG is defined

Fix below errors when the item DISABLE_MON_CONFIG is defined:
No return value for below two APIs:
dp_tx_mon_buf_refill() and dp_rx_mon_buf_refill()

CRs-Fixed: 3205083
Change-Id: If449616e30e75c23c7b25fb449a0ad8e501529aa

dp/wifi3.0/monitor/dp_mon.h

@@ -2344,11 +2344,13 @@ dp_tx_mon_process(struct dp_soc *soc, struct dp_intr *int_ctx,
 static inline
 uint32_t dp_tx_mon_buf_refill(struct dp_intr *int_ctx)
 {
+	return 0;
 }
 
 static inline
 uint32_t dp_rx_mon_buf_refill(struct dp_intr *int_ctx)
 {
+	return 0;
 }
 #endif