freebsd_network: bus_size_t seems to always be no larger than void*.

FreeBSD seems to do this, too, and sets BUS_SPACE_MAXSIZE appropriately
(which it seems we already do.) Fixes 32-bit builds following previous
commits.

src/libs/compat/freebsd_network/compat/machine/_bus.h

@@ -10,7 +10,7 @@
 
 
 typedef phys_addr_t bus_addr_t;
-typedef phys_size_t bus_size_t;
+typedef size_t bus_size_t;
 typedef addr_t bus_space_handle_t;