liquidio: Use pcie_flr() instead of reimplementing it

octeon_mbox_process_cmd() directly writes the PCI_EXP_DEVCTL_BCR_FLR
bit, which bypasses timing requirements imposed by the PCIe spec.
This patch fixes the function to use the pcie_flr() interface instead.

Signed-off-by: Denis Efremov <efremov@linux.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>