regulator: fixed-helper: use the correct function name in comment

Use the correct function name and modify the function short description.
This prevents a kernel-doc warning:

drivers/regulator/fixed-helper.c:32: warning: expecting prototype for regulator_register_fixed_name(). Prototype was for regulator_register_always_on() instead
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230113064421.11986-1-rdunlap@infradead.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/fixed-helper.c

@@ -20,7 +20,7 @@ static void regulator_fixed_release(struct device *dev)
 }
 
 /**
- * regulator_register_fixed_name - register a no-op fixed regulator
+ * regulator_register_always_on - register an always-on regulator with a fixed name
  * @id: platform device id
  * @name: name to be used for the regulator
  * @supplies: consumers for this regulator