PM / devfreq: tegra20: add COMMON_CLK dependency

Compile-testing the new driver on platforms without CONFIG_COMMON_CLK
leads to a link error:

drivers/devfreq/tegra20-devfreq.o: In function `tegra_devfreq_target':
tegra20-devfreq.c:(.text+0x288): undefined reference to `clk_set_min_rate'

Add a dependency on COMMON_CLK to avoid this.

Fixes: 1d39ee8dad6d ("PM / devfreq: Introduce driver for NVIDIA Tegra20")
Signed-off-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Dmitry Osipenko <[e-mail]>
Reviewed-by: Chanwoo Choi <[e-mail]>
Signed-off-by: MyungJoo Ham <[e-mail]>

drivers/devfreq/Kconfig

···
 config ARM_TEGRA20_DEVFREQ
 	tristate "NVIDIA Tegra20 DEVFREQ Driver"
 	depends on (TEGRA_MC && TEGRA20_EMC) || COMPILE_TEST
+	depends on COMMON_CLK
 	select DEVFREQ_GOV_SIMPLE_ONDEMAND
 	select PM_OPP
 	help