powerpc/pci: Fix unmapping of IO space on 64-bit

A typo/thinko made us pass the wrong argument to __flush_hash_table_range
when unplugging bridges, thus not flushing all the translations for
the IO space on unplug.  The third parameter to __flush_hash_table_range
is `end', not `size'.

This causes the hypervisor to refuse unplugging slots.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>