ALSA: add/change some comments describing function return values

script/kernel-doc reports the following type of warnings (when run in verbose
mode):

Warning(sound/core/init.c:152): No description found for return value of
'snd_card_create'

To fix that:
- add missing descriptions of function return values
- use "Return:" sections to describe those return values

Along the way:
- complete some descriptions
- fix some typos

Signed-off-by: Yacine Belkadi <yacine.belkadi.1@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/isadma.c

@@ -81,7 +81,7 @@ EXPORT_SYMBOL(snd_dma_disable);
  * @dma: the dma number
  * @size: the dma transfer size
  *
- * Returns the current pointer in DMA tranfer buffer in bytes
+ * Return: The current pointer in DMA transfer buffer in bytes.
  */
 unsigned int snd_dma_pointer(unsigned long dma, unsigned int size)
 {