libnvdimm: fix badblock range handling of ARS range

__add_badblock_range() does not account sector alignment when
it sets 'num_sectors'.  Therefore, an ARS error record range
spanning across two sectors is set to a single sector length,
which leaves the 2nd sector unprotected.

Change __add_badblock_range() to set 'num_sectors' properly.

Cc: <stable@vger.kernel.org>
Fixes: 0caeef63 ("libnvdimm: Add a poison list and export badblocks")
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>