ALSA backend: Fix a '|' precedence warning

Found by Clang 14 on FreeBSD CI:

kmix/backends/mixer_alsa9.cpp:473:9: warning: operator '?:' has lower
precedence than '|'; '|' will be evaluated first [-Wbitwise-conditional-parentheses]
        ? snd_mixer_selem_has_capture_switch ( elem )
        ^
kmix/backends/mixer_alsa9.cpp:473:9: note: place parentheses around
the '|' expression to silence this warning
        ? snd_mixer_selem_has_capture_switch ( elem )
        ^
kmix/backends/mixer_alsa9.cpp:473:9: note: place parentheses around
the '?:' expression to evaluate it first
        ? snd_mixer_selem_has_capture_switch ( elem )
        ^