aplay: Fix uninterruptible aplay

aplay: Fix uninterruptible aplay

When aplay is invoked to play from stdin, it can't be terminated by
normal signals like SIGTERM or SIGINT.  It's because our signal
handler tries to trap as much as possible while the stalling point is
not in the PCM loop but rather the file I/O.

For fixing this, leave our signal handler once when a signal is
received and snd_pcm_abort() is called.  At the next hit, it shall be
handled normally.

Signed-off-by: Takashi Iwai <tiwai@suse.de>