Fix find_inverse.c so that it generates a correct table.

For signed i32 division by 209, it was inaccurately accepting a multiply
by 1315205297 and a shift by 6 for that, even though the correct result
is 2630410593 and 7.   Now, it does 10x more random samples of values,
which is enough to generate a correct result.

(The checked in table is correct, though; presumably it was generated
with a different version of find_inverse.  Sending this patch in to
avoid trouble in the future.)