[syzbot] KASAN: null-ptr-deref Write in snd_pcm_format_set_silence

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+205eb15961852c2c5974 at syzkaller.appspotmail.com

Tested on:

commit:         1a3b1bba Merge tag 'nfs-for-5.18-2' of git://git.linux..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=df0c3f2244c64190
dashboard link: https://syzkaller.appspot.com/bug?extid=205eb15961852c2c5974
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17fb5d30f00000

Note: testing is done by a robot and is best-effort only.