regulator: core.c: Improve a comment

s/regulator may on/regulator may already be enabled/
s/or left on/or was left on/

The aim of this patch is to make the comment more readable and to make
it clear, that this is about a regulator, that is already enabled instead
of a regulator that may be switched on.

Signed-off-by: Sebastian Fricke <sebastian.fricke@posteo.net>
Link: https://lore.kernel.org/r/20210421055236.13148-1-sebastian.fricke@posteo.net
Signed-off-by: Mark Brown <broonie@kernel.org>