sound tests: Fix 32bit calculation detection in pcm_read_write

[dev_submerge.ch]

Summary

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.

MFC after: 1 week

[dev_submerge.ch]

To the best of my knowledge, this should fix the test on i386. I haven't spotted any other test failures yet on CI, but that's not conclusive - some architectures seem to have build failures and won't run the tests.

[christos]

LGTM. I just saw that https://ci.freebsd.org/job/FreeBSD-main-i386-test/lastUnstableBuild/testReport/junit/sys.sound/pcm_read_write/pcm_read/ reported this error, as a result of the 32 -> 24 bit conversion not happening.

EDIT: Seems like you linked to this as well yesterday. :-)