PCI/ACPI: Update link to PCI firmware specification

The previous link to the PCI firmware specification in the comments
for drivers/pci/pci-acpi.c no longer works.  Update the comment
to a current link to this specification.

Link: https://lore.kernel.org/r/20220722174754.27921-1-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: superm1

drivers/pci/pci-acpi.c

@@ -21,8 +21,9 @@
 #include "pci.h"
 
 /*
- * The GUID is defined in the PCI Firmware Specification available here:
- * https://www.pcisig.com/members/downloads/pcifw_r3_1_13Dec10.pdf
+ * The GUID is defined in the PCI Firmware Specification available
+ * here to PCI-SIG members:
+ * https://members.pcisig.com/wg/PCI-SIG/document/15350
  */
 const guid_t pci_acpi_dsm_guid =
 	GUID_INIT(0xe5c937d0, 0x3553, 0x4d7a,