ao_coreaudio_utils: don't list some formats as "unusable"

While mpv has no internal equivalent representation, they can still be
used as physical CoreAudio formats. Thus this label is confusing.

(cherry picked from commit 1bcb82ec93)

audio/out/ao_coreaudio_utils.c

@@ -258,7 +258,7 @@ void ca_print_asbd(struct ao *ao, const char *description,
        (flags & kAudioFormatFlagIsPacked) ? " packed" : "",
        (flags & kAudioFormatFlagIsAlignedHigh) ? " aligned" : "",
        (flags & kAudioFormatFlagIsNonInterleaved) ? " P" : "",
-       mpfmt ? af_fmt_to_str(mpfmt) : "unusable");
+       mpfmt ? af_fmt_to_str(mpfmt) : "-");
 }
 
 // Return whether new is an improvement over old. Assume a higher value means