Staging: usb-ip: vhci_hdc:Fix the returned error value

Compared with other drivers, the "ret" should be nagative and
returned. But in vhci_hdc, it always return 0;

I dont't use the driver, and I'm not familiar with the code.
Hope the patch is helpful.

Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>