generic: fix appended dtb support

Appended DTB support is mostly intended to be used on legacy systems,
but it is a valid feature that can be enabled for generic platform,
which currently doesn't support it - if selected, the appended DTB will
be ignored by the platform startup code.

During kernel startup, the appended DTB's location is stored in
fw_passed_dtb if the init code finds what appears to be a valid DTB.
Otherwise (if a0 == -2), a1 is stored in fw_passed_dtb, so either way it
will always point to either a user-passed DTB or built-in DTB.
Signed-off-by: Marcin Nowakowski <marcin.nowakowski@fungible.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org

arch/mips/generic/init.c

@@ -43,14 +43,14 @@ void __init *plat_get_fdt(void)
 		/* Already set up */
 		return (void *)fdt;
 
-	if ((fw_arg0 == -2) && !fdt_check_header((void *)fw_arg1)) {
+	if ((fw_arg0 == -2) && !fdt_check_header((void *)fw_passed_dtb)) {
 		/*
 		 * We booted using the UHI boot protocol, so we have been
 		 * provided with the appropriate device tree for the board.
 		 * Make use of it & search for any machine struct based upon
 		 * the root compatible string.
 		 */
-		fdt = (void *)fw_arg1;
+		fdt = (void *)fw_passed_dtb;
 
 		for_each_mips_machine(check_mach) {
 			match = mips_machine_is_compatible(check_mach, fdt);