regulator: cpr-regulator: fix of_property_read_bool() usage

The function of_property_read_bool() is used in several places
in the cpr-regulator driver to test for the existence of
non-boolean device tree properties.  These calls will work as
expected; however, of_property_read_bool() is only meant to be
used for reading boolean device tree properties.

Replace all usages of of_property_read_bool() which test for
non-boolean property existence with of_find_property().

Change-Id: Icafaa209443d9fd24b5bbbc023c1fb70f9928249
Signed-off-by: David Collins <collinsd@codeaurora.org>