usbip: fix vhci_hcd controller counting

Without this usbip fails on a machine with devices
that lexicographically come after vhci_hcd.

ie.
  $ ls -l /sys/devices/platform
  ...
  drwxr-xr-x. 4 root root    0 Sep 19 16:21 serial8250
  -rw-r--r--. 1 root root 4096 Sep 19 23:50 uevent
  drwxr-xr-x. 6 root root    0 Sep 20 13:15 vhci_hcd.0
  drwxr-xr-x. 4 root root    0 Sep 19 16:22 w83627hf.656

Because it detects 'w83627hf.656' as another vhci_hcd controller,
and then fails to be able to talk to it.

Note: this doesn't actually fix usbip's support for multiple
controllers... that's still broken for other reasons
("vhci_hcd.0" is hardcoded in a string macro), but is enough to
actually make it work on the above machine.

See also:
  https://bugzilla.redhat.com/show_bug.cgi?id=1631148



Cc: Jonathan Dieter <jdieter@gmail.com>
Cc: Valentina Manea <valentina.manea.m@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Maciej Żenczykowski <zenczykowski@gmail.com>
Acked-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Tested-by: Jonathan Dieter <jdieter@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>