USB: cdc-wdm: avoid printing odd-looking "cdc-wdm-176" names

usb_register_dev() will change our .minor_base to 0 if
CONFIG_USB_DYNAMIC_MINORS is set.  And it usually is, of
course.

Use dev_name() to print the proper interface name instead

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>