MIPS: boot: Fix unaligned access with CONFIG_MIPS_RAW_APPENDED_DTB

commit 4d4f9c1a upstream.

The compressed payload is not necesarily 4-byte aligned, at least when
compiling with Clang. In that case, the 4-byte value appended to the
compressed payload that corresponds to the uncompressed kernel image
size must be read using get_unaligned_le32().

This fixes Clang-built kernels not booting on MIPS (tested on a Ingenic
JZ4770 board).

Fixes: b8f54f2c

 ("MIPS: ZBOOT: copy appended dtb to the end of the kernel")
Cc: <stable@vger.kernel.org> # v4.7
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>