USB: legousbtower: fix a signedness bug in tower_probe()

The problem is that sizeof() is unsigned long so negative error codes
are type promoted to high positive values and the condition becomes
false.

Fixes: 1d427be4

 ("USB: legousbtower: fix slab info leak at probe")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191011141115.GA4521@mwanda


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