ARM: mach-omap2: Kconfig: Make SYS_MPUCLK dependent on AM33XX

This value is unly used in arch/arm/mach-omap2/am33xx/
clock_am33xx.c, so let's make it dependent on AM33XX since
that is the only way this file gets compiled into the code
according to the Makefile.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Fix symbol name]
Signed-off-by: Tom Rini <trini@konsulko.com>

arch/arm/mach-omap2/Kconfig

@@ -136,6 +136,7 @@ endchoice
 
 config SYS_MPUCLK
 	int "MPU CLK speed"
+	depends on AM33XX
 	default 500
 	help
 	  Defines the MPU clock speed (in MHz).