regulator: use of_property_read_{bool|u32}()

Use more compact of_property_read_{bool|u32}() calls instead of the
of_{find|get}_property() calls in of_get_regulation_constraints() where
possible (note that of_property_read_{bool|u32}() were already used to read
some properties).

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Mark Brown <broonie@linaro.org>