ARM: uniphier: do not overwrite fdt_file environment

This code auto-detects the best-match FDT file name, but it should
respect the user's choice if "fdt_file" environment is found in a
saved set of environments.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/mach-uniphier/board_late_init.c

@@ -39,6 +39,9 @@ static int uniphier_set_fdt_file(void)
 	int buf_len = 256;
 	int ret;
 
+	if (getenv("fdt_file"))
+		return 0;	/* do nothing if it is already set */
+
 	ret = fdt_get_string(gd->fdt_blob, 0, "compatible", &compat);
 	if (ret)
 		return -EINVAL;