boot_fit: Change return value from FDT_ERROR to -EINVAL in fdt_offset()

FDT_ERROR is defined as unsigned long. However, since the return value of
fdt_offset() is int, a warning will occur when compiling. Also, it is better
to use -EINVAL than FDT_ERROR.
This fixes this problem by change return value from FDT_ERROR to -EINVAL.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
CC: Franklin S Cooper Jr <fcooper@ti.com>
Reviewed-by: Franklin S Cooper Jr <fcooper@ti.com>

common/boot_fit.c

@@ -25,7 +25,7 @@ int fdt_offset(void *fit)
 	images = fdt_path_offset(fit, FIT_IMAGES_PATH);
 	if (images < 0) {
 		debug("%s: Cannot find /images node: %d\n", __func__, images);
-		return FDT_ERROR;
+		return -EINVAL;
 	}
 
 	fdt_name = fdt_getprop(fit, node, FIT_FDT_PROP, &fdt_len);