USB: rename Documentation/ABI/.../sysfs-class-usb_host

The usb_host class is no more.  Rename its documentation file (which
only contained WUSB specific files) to .../sysfs-class-uwb_rc-wusbhc.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>