libnvdimm: release ida resources

ida instances allocate some internal memory for ->free_bitmap in
addition to the base 'struct ida'.  Use ida_destroy() to release that
memory at module_exit().

Reported-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>