lib/math/test_div64: Fix error message formatting

Align the expected result with one actually produced for easier visual
comparison; this has to take into account what the format specifiers
will actually produce rather than the characters they consist of.  E.g.:

test_div64: ERROR: 10000000ab275080 / 00000009 => 01c71c71da20d00e,00000002
test_div64: ERROR: expected value              => 0000000013045e47,00000001

(with a failure induced by setting bit #60 of the divident).

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>