ALSA: lola: add a check for the return of vmalloc()

vmalloc() is a memory allocation function which can return NULL when
some internal memory errors happen. So it is better to check the return
of it to catch the error in time.

Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Link: https://lore.kernel.org/r/tencent_4221FC4089F6DF01C48F192E5784038BA205@qq.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>