clk: versatile: make config option boolean

There is no choice to have the RealView clocks as module for sure,
so turn this config option into a boolean.
Reported-by: NPawel Moll <pawel.moll@arm.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NMike Turquette <mturquette@linaro.org>

drivers/clk/Kconfig

@@ -41,7 +41,7 @@ config COMMON_CLK_WM831X
 	  PMICs from Wolfson Microlectronics.
 
 config COMMON_CLK_VERSATILE
-	tristate "Clock driver for ARM Reference designs"
+	bool "Clock driver for ARM Reference designs"
 	depends on ARCH_INTEGRATOR || ARCH_REALVIEW
 	---help---
           Supports clocking on ARM Reference designs Integrator/AP,