[MTD] physmap: fix leak of memory returned by parse_mtd_partitions

The mtd partition parser returns an allocated pointer array of
mtd_partition.  The caller must free it.  The array is used only for
add_mtd_partitions(), so free it just after the call.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>