ALSA: es1938: check snd_ctl_new1() return value

ALSA: es1938: check snd_ctl_new1() return value

snd_ctl_new1() can return NULL when memory allocation fails.
snd_es1938_mixer() does not check the return value before dereferencing
the pointer, 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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Zhao Dongdong <zhaodongdong@kylinos.cn>
Link: https://patch.msgid.link/tencent_E0DC65165FDF2C8982BAFB6794B854B53B0A@qq.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>