Export dm_table_get_size.

Combine with snapshot patch.
--- diff/drivers/md/dm-table.c	2005-05-05 14:32:08.000000000 +0100
+++ source/drivers/md/dm-table.c	2005-05-05 14:31:54.000000000 +0100
@@ -943,6 +943,7 @@
 EXPORT_SYMBOL(dm_get_device);
 EXPORT_SYMBOL(dm_put_device);
 EXPORT_SYMBOL(dm_table_event);
+EXPORT_SYMBOL(dm_table_get_size);
 EXPORT_SYMBOL(dm_table_get_mode);
 EXPORT_SYMBOL(dm_table_put);
 EXPORT_SYMBOL(dm_table_get);