cmd: efidebug: fix a wrong handling of arguments

Coverity detected a dead code, but actually there is a bug in a check
against a number of arguments. So simply fix it.

Reported-by: Coverity (CID 300330)
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

cmd/efidebug.c

@@ -602,7 +602,7 @@ static int do_efi_boot_add(cmd_tbl_t *cmdtp, int flag,
 				+ sizeof(struct efi_device_path); /* for END */
 
 	/* optional data */
-	if (argc < 6)
+	if (argc == 6)
 		lo.optional_data = NULL;
 	else
 		lo.optional_data = (const u8 *)argv[6];