USB: whci-hcd: fix NULL dereference on allocation failure

If usb_create_hcd() fails here then we dereference "whc" inside the call
to whc_clean_up() before it has been set.  The compiler would have
warned about this if we hadn't initialized all the pointers to NULL at
the start of the function.  I've cleaned that up as well.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>