usbip: vhci-hcd: Rename function names to reflect their struct names

These helper function names are renamed to have their full struct
names to avoid confusion:

 - hcd_to_vhci() -> hcd_to_vhci_hcd()
 - vhci_to_hcd() -> vhci_hcd_to_hcd()
 - vdev_to_vhci() -> vdev_to_vhci_hcd()

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>