ALSA: doc: Drop snd_dma_continuous_data() usages

Update the documentation to follow the recent change of the memory
allocation helpers.  The macro snd_dma_continuous_data() is gone, and
the driver needs to set up the coherent dma mask for allocating in the
lower memory addresses, instead.

Link: https://lore.kernel.org/r/20220823115740.14123-6-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/kernel-api/writing-an-alsa-driver.rst

@@ -3565,13 +3565,17 @@ given size.
 The second argument (type) and the third argument (device pointer) are
 dependent on the bus. For normal devices, pass the device pointer
 (typically identical as ``card->dev``) to the third argument with
-``SNDRV_DMA_TYPE_DEV`` type. For the continuous buffer unrelated to the
+``SNDRV_DMA_TYPE_DEV`` type.
+
+For the continuous buffer unrelated to the
 bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type.
 You can pass NULL to the device pointer in that case, which is the
 default mode implying to allocate with ``GFP_KERNEL`` flag.
-If you need a different GFP flag, you can pass it by encoding the flag
-into the device pointer via a special macro
-:c:func:`snd_dma_continuous_data()`.
+If you need a restricted (lower) address, set up the coherent DMA mask
+bits for the device, and pass the device pointer, like the normal
+device memory allocations.  For this type, it's still allowed to pass
+NULL to the device pointer, too, if no address restriction is needed.
+
 For the scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with the
 device pointer (see the `Non-Contiguous Buffers`_ section).
 
@@ -3811,15 +3815,6 @@ arguments here.  Since each vmalloc call should succeed at any time,
 we don't need to pre-allocate the buffers like other continuous
 pages.
 
-If you need the 32bit DMA allocation, pass the device pointer encoded
-by :c:func:`snd_dma_continuous_data()` with ``GFP_KERNEL|__GFP_DMA32``
-argument.
-
-::
-
-  snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC,
-          snd_dma_continuous_data(GFP_KERNEL | __GFP_DMA32), 0, 0);
-
 Proc Interface
 ==============