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

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.org
Signed-off-by: Mark Brown <broonie@kernel.org>