pcm_file: do not disrupt playback on output file write fail

pcm_file: do not disrupt playback on output file write fail

previously playback could be interrupted by snd_pcm_file_add_frames:
    assert(file->wbuf_used_bytes < file->wbuf_size_bytes)

in case snd_pcm_file_write_bytes fails to write full amount of bytes
to file, variable wbuf_used_bytes would not be fully decremented by
requested amount of bytes function was called with

for the assert to trigger, multiple write fails need to happen, so
that wbuf_used_bytes overflows wbuf_size_bytes,

this patch will allow application to report error code to api user
who might have an idea how to recover, before assert is triggered,
also reporting error along with the print out message might give user
a better idea of what is going on, where previously reason for
mentioned assert was not immediately clear

Signed-off-by: Adam Miartus <amiartus@de.adit-jv.com>
Reviewed-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>