USB: lvtest: return proper error code in probe

lvs_rh_probe() can return some nonnegative value from usb_control_msg()
when it is less than "USB_DT_HUB_NONVAR_SIZE + 2" that is considered as
a failure. Make lvs_rh_probe() return -EINVAL in this case.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Evgeny Novikov <novikov@ispras.ru>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200805090643.3432-1-novikov@ispras.ru


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>