PCI: remove additional pci_scan_child_bus() prototype

There's already a prototype for pci_scan_child_bus() at the correct place in
pci.h, so there's no reason for an additional one.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>