usbip: vhci-hcd: make vhci_hc_driver const

Make this const as it is not modified anywhere.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>