PCI: Clarify PCI_EXP_TYPE_PCI_BRIDGE comment

The PCI_EXP_TYPE_PCI_BRIDGE is a *PCIe* function that is a bridge to
PCI/PCI-X.  See PCIe spec r3.0, sec 7.8.2.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

include/uapi/linux/pci_regs.h

@@ -421,8 +421,8 @@
 #define  PCI_EXP_TYPE_ROOT_PORT 0x4	/* Root Port */
 #define  PCI_EXP_TYPE_UPSTREAM	0x5	/* Upstream Port */
 #define  PCI_EXP_TYPE_DOWNSTREAM 0x6	/* Downstream Port */
-#define  PCI_EXP_TYPE_PCI_BRIDGE 0x7	/* PCI/PCI-X Bridge */
-#define  PCI_EXP_TYPE_PCIE_BRIDGE 0x8	/* PCI/PCI-X to PCIE Bridge */
+#define  PCI_EXP_TYPE_PCI_BRIDGE 0x7	/* PCIe to PCI/PCI-X Bridge */
+#define  PCI_EXP_TYPE_PCIE_BRIDGE 0x8	/* PCI/PCI-X to PCIe Bridge */
 #define  PCI_EXP_TYPE_RC_END	0x9	/* Root Complex Integrated Endpoint */
 #define  PCI_EXP_TYPE_RC_EC	0xa	/* Root Complex Event Collector */
 #define PCI_EXP_FLAGS_SLOT	0x0100	/* Slot implemented */