ALSA: ppc: beep: fix clang -Wimplicit-fallthrough

ALSA: ppc: beep: fix clang -Wimplicit-fallthrough

Clang warns:

sound/ppc/beep.c:103:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
        case SND_TONE: break;
        ^
sound/ppc/beep.c:103:2: note: insert 'break;' to avoid fall-through
        case SND_TONE: break;
        ^
        break;
1 warning generated.

Clang is more pedantic than GCC, which does not warn when failing
through to a case that is just break or return. Clang's version
is more in line with the kernel's own stance in deprecated.rst.
Add athe missing break to silence the warning.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Link: https://lore.kernel.org/r/20211207110053.695712-1-anders.roxell@linaro.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>