ALSA: pcm: oss: Remove superfluous WARN_ON() for mulaw sanity check

ALSA: pcm: oss: Remove superfluous WARN_ON() for mulaw sanity check

The PCM OSS mulaw plugin has a check of the format of the counter part
whether it's a linear format.  The check is with snd_BUG_ON() that
emits WARN_ON() when the debug config is set, and it confuses
syzkaller as if it were a serious issue.  Let's drop snd_BUG_ON() for
avoiding that.

While we're at it, correct the error code to a more suitable, EINVAL.

Reported-by: syzbot+23b22dc2e0b81cbfcc95@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200901131802.18157-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>