qcacmn: Do not allocate 0 byte memory in DFS component

In DFS component 0 byte memory is allocated when dfs_nol_count is 0.
We see a print 'allocating 0 bytes at this location' during wifi unload.

Change-Id: I5d6ad36875d634ee5ae6a138656bdb3f538bcdbe
CRs-Fixed: 2316513

umac/dfs/core/src/misc/dfs_nol.c

@@ -475,6 +475,11 @@ void dfs_nol_update(struct wlan_dfs *dfs)
 	struct dfsreq_nolelem *dfs_nol;
 	int nlen;
 
+	if (!dfs->dfs_nol_count) {
+		dfs_debug(dfs, WLAN_DEBUG_DFS_NOL, "dfs_nol_count is zero");
+		return;
+	}
+
 	/*
 	 * Allocate enough entries to store the NOL. At least on Linux
 	 * (don't ask why), if you allocate a 0 entry array, the