qcom: msm-clock-controller: Remove incorrect usage of_property_read_bool

of_property_read_bool is really only meant to check if
a boolean property has been set. Although its implementation
has been simplified to just check for the existence of
the property, it is meant to be used only when the property
in question is actually a boolean. Furthermore, one cannot
guarantee that the underlying implementation will remain
the same forever. To check if a property exists, use the
of_find_property API.

Change-Id: I2f1c60bd9389b29f251b267c36e5d07eddf749f4
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>