USB: wusb: check CHID is all zeros before stopping the host

An incorrect sizeof() resulted in only 4 (or 8) octets of the CHID being
checked instead of all 16 octets.  A randomly generated CHID had a
probability of being unable to start a WUSB host of less than 1 in
2 billion.

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