regulator: Minor regulator documentation fixes.

The newly added regulator ramp-delay specifiers in regulator desc
lacked the documentation. Add some. Also fix a typo.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/20210818041513.GA2408290@dc7vkhyh15000m40t6jht-3.rev.dnainternet.fi
Signed-off-by: Mark Brown <broonie@kernel.org>