mtd: mips: lantiq: reintroduce support for cmdline partitions

Since commit ca97dec2 the
command line parsing of MTD partitions does not work anymore.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: stable@kernel.org [3.2+]
Acked-by: John Crispin <blogic@openwrt.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>