[pci] Allow pci_vpd_init() return status to be ignored

Most xxx_init() functions are void functions with no failure cases.
Allow pci_vpd_init() to be used in the same way.  (Subsequent calls to
pci_vpd_read() etc. will fail if pci_vpd_init() fails.)

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/pcivpd.h

@@ -133,6 +133,17 @@ struct pci_vpd {
 	struct pci_vpd_cache cache;
 };
 
+/**
+ * Check for presence of PCI VPD
+ *
+ * @v vpd		PCI VPD
+ * @ret is_present	VPD is present
+ */
+static inline __attribute__ (( always_inline )) int
+pci_vpd_is_present ( struct pci_vpd *vpd ) {
+	return ( vpd->cap != 0 );
+}
+
 /**
  * Check if PCI VPD read cache is valid
  *