pci_bus_find_capability() is decleared in pci.h, so it is not necessary to do
it again.

This patch removes it.
Signed-off-by: NWei Yang <weiyang@linux.vnet.ibm.com>
Reviewed-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>