microblaze/PCI: Remove unnecessary pci_bus_find_capability() declaration

pci_bus_find_capability() is declared in include/linux/pci.h.

Remove the pci_bus_find_capability() declaration from
arch/microblaze/include/asm/pci.h.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Michal Simek <monstr@monstr.eu>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>