dt-bindings: opp: Increase maxItems for opp-hz property

Current limit of 16 will be exhausted by platforms specifying the frequency
for 9 clocks using opp-hz, like Qcom SDM845 SoC. For instance, specifying
the frequency for 9 clocks with 64bit specifier as below would consume
(9 * 2 = 18) items.

	opp-50000000 {
		opp-hz = /bits/ 64 <50000000>,
			 /bits/ 64 <0>,
			 /bits/ 64 <0>,
			 /bits/ 64 <37500000>,
			 /bits/ 64 <0>,
			 /bits/ 64 <0>,
			 /bits/ 64 <0>,
			 /bits/ 64 <0>,
			 /bits/ 64 <75000000>;
	};

So let's increase the limit to 32 which should be enough for most platforms
(hopefully).

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>