cpufreq: tegra20: Check if this is Tegra20 machine

Don't even try to request the clocks during of module initialization on
non-Tegra20 machines (this is the case for a multi-platform kernel) for
consistency.
Signed-off-by: NDmitry Osipenko <digetx@gmail.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/tegra20-cpufreq.c

@@ -21,6 +21,7 @@
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/of.h>
 #include <linux/types.h>
 
 static struct cpufreq_frequency_table freq_table[] = {
@@ -158,6 +159,9 @@ static int __init tegra_cpufreq_init(void)
 {
 	int err;
 
+	if (!of_machine_is_compatible("nvidia,tegra20"))
+		return -ENODEV;
+
 	cpu_clk = clk_get_sys(NULL, "cclk");
 	if (IS_ERR(cpu_clk))
 		return PTR_ERR(cpu_clk);