mips: txx9: fix iounmap related issue

if device_register return error, iounmap should be called, also iounmap
need to call before put_device.

Signed-off-by: Ding Xiang <dingxiang@cmss.chinamobile.com>
Reviewed-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20476/
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org