parse: don't check for < 0 on an unsigned type

parse: don't check for < 0 on an unsigned type

We do strict errors on some builds, this breaks them. Remove the
<= 0 check, just check for a value that's too large.

Fixes: c26438ad ("parse: dump option type when using --debug=parse")
Signed-off-by: Jens Axboe <axboe@kernel.dk>