brcmfmac: remove 'always false' condition from brcmf_c_mkiovar_bsscfg

The parameter buflen is unsigned so the condition buflen < 0 is
always false. The patch fixes the if statement checking the buffer
length.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NPieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: NHante Meuleman <meuleman@broadcom.com>
Signed-off-by: NArend van Spriel <arend@broadcom.com>
Signed-off-by: NFranky Lin <frankyl@broadcom.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/brcm80211/brcmfmac/dhd_common.c

@@ -106,7 +106,7 @@ brcmf_c_mkiovar_bsscfg(char *name, char *data, uint datalen,
 	namelen = (u32) strlen(name) + 1; /* lengh of iovar  name + null */
 	iolen = prefixlen + namelen + sizeof(bssidx_le) + datalen;
 
-	if (buflen < 0 || iolen > (u32)buflen) {
+	if ((u32)buflen < iolen) {
 		brcmf_dbg(ERROR, "buffer is too short\n");
 		return 0;
 	}