cpufreq: sun50i: fix error returns in dt_has_supported_hw()

The dt_has_supported_hw() function returns type bool.  That means these
negative error codes are cast to true but the function should return
false instead.

Fixes: fa5aec95 ("cpufreq: sun50i: Add support for opp_supported_hw")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>