A recent patch updated the name of pci_assign_all_busses to
pci_assign_all_buses.  This instance of its use wasn't corrected
by the original patch to use the new name.

Builds cleanly on ads8272.
Signed-off-by: Becky Bruce <becky.bruce@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>