nb/intel/haswell/pcie.c: Fix getting PCI function

Use `dev->path.pci.devfn` to obtain the `devfn` that `PCI_FUNC` needs.

Tested on Asrock B85M Pro4, `PCI_FUNC` now obtains the correct value.

Change-Id: Ia3bbd56ce0adba9d24f62ffc016cd825bcf3cc6a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55688
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/northbridge/intel/haswell/pcie.c

@@ -50,7 +50,7 @@ static void peg_enable(struct device *dev)
 {
 	const struct northbridge_intel_haswell_config *config = config_of(dev);
 
-	const uint8_t func = PCI_FUNC(PCI_BDF(dev));
+	const uint8_t func = PCI_FUNC(dev->path.pci.devfn);
 
 	assert(func < ARRAY_SIZE(config->peg_cfg));