PCI-IOV: fix missing kernel-doc

Fix PCI iov kernel-doc warning:

Warning(drivers/pci/iov.c:638): No description found for parameter 'nr_virtfn'

Signed-off-by: Randy Dunlap <[e-mail]>
Signed-off-by: Jesse Barnes <[e-mail]>

drivers/pci/iov.c

···
 /**
  * pci_enable_sriov - enable the SR-IOV capability
  * @dev: the PCI device
+ * @nr_virtfn: number of virtual functions to enable
  *
  * Returns 0 on success, or negative on failure.
  */