regulator: proxy-consumer: fix of_property_read_bool() usage

The function of_property_read_bool() is used in the
proxy-consumer driver to test for the existence of non-boolean
device tree properties qcom,proxy-consumer-voltage and
qcom,proxy-consumer-current.  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: I83a718d05f5495f514d6a70004fcb5a2780d45c0
Signed-off-by: David Collins <collinsd@codeaurora.org>