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>

include/sound/control.h

@@ -189,7 +189,6 @@ int _snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave,
  *
  * Add a virtual slave control to the given master element created via
  * snd_ctl_create_virtual_master() beforehand.
- * Returns zero if successful or a negative error code.
  *
  * All slaves must be the same type (returning the same information
  * via info callback).  The function doesn't check it, so it's your
@@ -199,6 +198,8 @@ int _snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave,
  * at most two channels,
  * logarithmic volume control (dB level) thus no linear volume,
  * master can only attenuate the volume without gain
+ *
+ * Return: Zero if successful or a negative error code.
  */
 static inline int
 snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave)
@@ -219,6 +220,8 @@ snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave)
  * When the control peeks the hardware values directly and the value
  * can be changed by other means than the put callback of the element,
  * this function should be used to keep the value always up-to-date.
+ *
+ * Return: Zero if successful or a negative error code.
  */
 static inline int
 snd_ctl_add_slave_uncached(struct snd_kcontrol *master,