MIPS: Lantiq: Fix MTD registration of NOR device

The 2 functions add_mtd_partitions and del_mtd_partitions were renamed to
mtd_device_register and mtd_device_unregister.

Signed-of-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2463/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>