gpio: qpnp-gpio: switch all dt property calls to of_property_read_u32

of_get_property() requires extra local variables and
handling. Switch to of_property_read_u32() since it simplifies
the code and is functionally equivalent.

Change-Id: If6d6d34ea3df8fb4135058d9a268ce8025a7fb03
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>