PCI: Use pci_wait_for_pending_transaction() instead of for loop

New routine has been added to avoid duplication of code to wait for
pending PCI transactions to complete.  This makes use of that function.

Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>