soc/amd/common/amd_pci_util.h: assign 0 to PIN_A in pcie_swizzle_pin

Explicitly assign a value of 0 to the first value of the
pcie_swizzle_pin enum. This won't change the behavior, but clarifies
that the actual values of the enum elements matter.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I21850e21f859f2079f804d4344a1a11856b27d90
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82049
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>

src/soc/amd/common/block/pci/pci_routing_info.c

@@ -7,7 +7,7 @@
 #include <types.h>
 
 enum pcie_swizzle_pin {
-	PIN_A,
+	PIN_A = 0,
 	PIN_B,
 	PIN_C,
 	PIN_D,