fdtdec: Update the missing-devicetree message

This includes information about sandbox which is not relevant for most
boards. Drop it.

Also add the address to help figure out the problem.

Signed-off-by: Simon Glass <sjg@chromium.org>

lib/fdtdec.c

@@ -600,7 +600,8 @@ int fdtdec_prepare_fdt(void)
 #ifdef CONFIG_SPL_BUILD
 		puts("Missing DTB\n");
 #else
-		puts("No valid device tree binary found - please append one to U-Boot binary, use u-boot-dtb.bin or define CONFIG_OF_EMBED. For sandbox, use -d <file.dtb>\n");
+		printf("No valid device tree binary found at %p\n",
+		       gd->fdt_blob);
 # ifdef DEBUG
 		if (gd->fdt_blob) {
 			printf("fdt_blob=%p\n", gd->fdt_blob);