PCI: remove useless pcix_set_mmrbc() dev->bus check

For a valid pci_dev, dev->bus != NULL always, so remove this
unnecessary test.

Found by Coverity (CID 101680).
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -3395,8 +3395,7 @@ int pcix_set_mmrbc(struct pci_dev *dev, int mmrbc)
 
 	o = (cmd & PCI_X_CMD_MAX_READ) >> 2;
 	if (o != v) {
-		if (v > o && dev->bus &&
-		   (dev->bus->bus_flags & PCI_BUS_FLAGS_NO_MMRBC))
+		if (v > o && (dev->bus->bus_flags & PCI_BUS_FLAGS_NO_MMRBC))
 			return -EIO;
 
 		cmd &= ~PCI_X_CMD_MAX_READ;