cmd: ubi: remove unreachable code

It does not make sense to check if argc < 2 a second time, especially after
accessing argv[1].
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>

cmd/ubi.c

@@ -472,12 +472,8 @@ static int do_ubi(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 	if (argc < 2)
 		return CMD_RET_USAGE;
 
-	if (strcmp(argv[1], "detach") == 0) {
-		if (argc < 2)
-			return CMD_RET_USAGE;
-
+	if (strcmp(argv[1], "detach") == 0)
 		return ubi_detach();
-	}
 
 	if (strcmp(argv[1], "part") == 0) {
 		const char *vid_header_offset = NULL;