ALSA: caiaq: Convert to the common vmalloc memalloc

The recent change (*) in the ALSA memalloc core allows us to drop the
special vmalloc-specific allocation and page handling.  This patch
coverts to the common code.
(*) 1fe7f397: ALSA: memalloc: Add vmalloc buffer allocation
                  support
    7e8edae3: ALSA: pcm: Handle special page mapping in the
                  default mmap handler

Link: https://lore.kernel.org/r/20191105151856.10785-13-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/caiaq/audio.c

@@ -170,15 +170,14 @@ static int snd_usb_caiaq_substream_close(struct snd_pcm_substream *substream)
 static int snd_usb_caiaq_pcm_hw_params(struct snd_pcm_substream *sub,
 				       struct snd_pcm_hw_params *hw_params)
 {
-	return snd_pcm_lib_alloc_vmalloc_buffer(sub,
-						params_buffer_bytes(hw_params));
+	return snd_pcm_lib_malloc_pages(sub, params_buffer_bytes(hw_params));
 }
 
 static int snd_usb_caiaq_pcm_hw_free(struct snd_pcm_substream *sub)
 {
 	struct snd_usb_caiaqdev *cdev = snd_pcm_substream_chip(sub);
 	deactivate_substream(cdev, sub);
-	return snd_pcm_lib_free_vmalloc_buffer(sub);
+	return snd_pcm_lib_free_pages(sub);
 }
 
 /* this should probably go upstream */
@@ -334,7 +333,6 @@ static const struct snd_pcm_ops snd_usb_caiaq_ops = {
 	.prepare =	snd_usb_caiaq_pcm_prepare,
 	.trigger =	snd_usb_caiaq_pcm_trigger,
 	.pointer =	snd_usb_caiaq_pcm_pointer,
-	.page =		snd_pcm_lib_get_vmalloc_page,
 };
 
 static void check_for_elapsed_periods(struct snd_usb_caiaqdev *cdev,
@@ -843,6 +841,8 @@ int snd_usb_caiaq_audio_init(struct snd_usb_caiaqdev *cdev)
 				&snd_usb_caiaq_ops);
 	snd_pcm_set_ops(cdev->pcm, SNDRV_PCM_STREAM_CAPTURE,
 				&snd_usb_caiaq_ops);
+	snd_pcm_lib_preallocate_pages_for_all(cdev->pcm, SNDRV_DMA_TYPE_VMALLOC,
+					      NULL, 0, 0);
 
 	cdev->data_cb_info =
 		kmalloc_array(N_URBS, sizeof(struct snd_usb_caiaq_cb_info),