ALSA: gus: check snd_ctl_new1() return value

ALSA: gus: check snd_ctl_new1() return value

snd_ctl_new1() can return NULL when memory allocation fails.
snd_gf1_pcm_volume_control() does not check the return value before
dereferencing kctl->id.index, which can lead to a NULL pointer
dereference.

Add a NULL check after snd_ctl_new1() and return -ENOMEM if it fails.

Assisted-by: Opencode:DeepSeek-V4-Flash
Cc: stable@vger.kernel.org
Fixes: c5ae57b1bb99 ("ALSA: gus: Fix kctl->id initialization")
Signed-off-by: Zhao Dongdong <zhaodongdong@kylinos.cn>
Link: https://patch.msgid.link/tencent_F644A3DCAD32945D62DB2FEEBE8A996F6809@qq.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>