regulator: tps65132-regulator: fix of_property_read_bool() usage

The function of_property_read_bool() is used in the
tps65132-regulator driver to test for the existence of
non-boolean device tree property i2c-pwr-supply.  This call will
work as expected; however, of_property_read_bool() is only meant
to be used for reading boolean device tree properties.

Replace this usage of of_property_read_bool() with
of_find_property().

Change-Id: I7f206d18db29899e04effea4a63c60f9ee5c1937
Signed-off-by: David Collins <collinsd@codeaurora.org>