PCI: correct pcie_set_readrq write size

When setting the PCI-E MRRS, pcie_set_readrq queries the current
settings via a pci_read_config_word call but writes the modified result
via a pci_write_config_dword.  This results in writing 16 more bits than
were queried.

Also, the function description comment is slightly incorrect.
Signed-off-by: NJon Mason <jdmason@kudzu.us>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/pci.c

@@ -3191,7 +3191,7 @@ EXPORT_SYMBOL(pcie_get_readrq);
  * @rq: maximum memory read count in bytes
  *    valid values are 128, 256, 512, 1024, 2048, 4096
  *
- * If possible sets maximum read byte count
+ * If possible sets maximum memory read request in bytes
  */
 int pcie_set_readrq(struct pci_dev *dev, int rq)
 {
@@ -3214,7 +3214,7 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
 	if ((ctl & PCI_EXP_DEVCTL_READRQ) != v) {
 		ctl &= ~PCI_EXP_DEVCTL_READRQ;
 		ctl |= v;
-		err = pci_write_config_dword(dev, cap + PCI_EXP_DEVCTL, ctl);
+		err = pci_write_config_word(dev, cap + PCI_EXP_DEVCTL, ctl);
 	}
 
 out: