sound tests: Fix 32bit calculation detection in pcm_read_write
Fix a mistake in the pcm_read_write test that would result in not
properly detecting 32bit calculation on 32bit architectures like i386.
As a consequence, the wrong values would be checked, thus failing the
test.
Reported by: CI
Fixes: 27ef5d48c729 ("sound: Unit test the pcm sample read and write macros")
MFC after: 1 week
Reviewed by: christos
Differential Revision: https://reviews.freebsd.org/D48617