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>
diff --git a/sound/sound_core.c b/sound/sound_core.c
index bb23009..359753f 100644
--- a/sound/sound_core.c
+++ b/sound/sound_core.c
@@ -352,7 +352,9 @@
  *      @dev: device pointer
  *
  *	Allocate a special sound device by minor number from the sound
- *	subsystem. The allocated number is returned on success. On failure
+ *	subsystem.
+ *
+ *	Return: The allocated number is returned on success. On failure,
  *	a negative error code is returned.
  */
  
@@ -436,8 +438,10 @@
  *	@dev: Unit number to allocate
  *
  *	Allocate a mixer device. Unit is the number of the mixer requested.
- *	Pass -1 to request the next free mixer unit. On success the allocated
- *	number is returned, on failure a negative error code is returned.
+ *	Pass -1 to request the next free mixer unit.
+ *
+ *	Return: On success, the allocated number is returned. On failure,
+ *	a negative error code is returned.
  */
 
 int register_sound_mixer(const struct file_operations *fops, int dev)
@@ -454,8 +458,10 @@
  *	@dev: Unit number to allocate
  *
  *	Allocate a midi device. Unit is the number of the midi device requested.
- *	Pass -1 to request the next free midi unit. On success the allocated
- *	number is returned, on failure a negative error code is returned.
+ *	Pass -1 to request the next free midi unit.
+ *
+ *	Return: On success, the allocated number is returned. On failure,
+ *	a negative error code is returned.
  */
 
 int register_sound_midi(const struct file_operations *fops, int dev)
@@ -477,11 +483,13 @@
  *	@dev: Unit number to allocate
  *
  *	Allocate a DSP device. Unit is the number of the DSP requested.
- *	Pass -1 to request the next free DSP unit. On success the allocated
- *	number is returned, on failure a negative error code is returned.
+ *	Pass -1 to request the next free DSP unit.
  *
  *	This function allocates both the audio and dsp device entries together
  *	and will always allocate them as a matching pair - eg dsp3/audio3
+ *
+ *	Return: On success, the allocated number is returned. On failure,
+ *	a negative error code is returned.
  */
 
 int register_sound_dsp(const struct file_operations *fops, int dev)