catch wrong load address passed to fatload / ext2load

If filename is passed instead of address to ext2load or fatload,
u-boot silently accepts that, and uses 0 for load address and default
filename from environment. That is confusing, display help instead.
Signed-off-by: NPavel Machek <pavel@denx.de>

fs/fs.c

@@ -276,6 +276,7 @@ int do_load(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
 	unsigned long pos;
 	int len_read;
 	unsigned long time;
+	char *ep;
 
 	if (argc < 2)
 		return CMD_RET_USAGE;
@@ -286,7 +287,9 @@ int do_load(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
 		return 1;
 
 	if (argc >= 4) {
-		addr = simple_strtoul(argv[3], NULL, 16);
+		addr = simple_strtoul(argv[3], &ep, 16);
+		if (ep == argv[3] || *ep != '\0')
+			return CMD_RET_USAGE;
 	} else {
 		addr_str = getenv("loadaddr");
 		if (addr_str != NULL)