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>

drivers/nvdimm/region_devs.c

@@ -793,3 +793,8 @@ struct nd_region *nvdimm_volatile_region_create(struct nvdimm_bus *nvdimm_bus,
 			__func__);
 }
 EXPORT_SYMBOL_GPL(nvdimm_volatile_region_create);
+
+void __exit nd_region_devs_exit(void)
+{
+	ida_destroy(&region_ida);
+}