ARM: msm: Only build clock.c on proc_comm based platforms

The functionality provided by clock.c in mach-msm is only needed
on proc_comm based platforms. Only build the file if proc_comm is
enabled. This prevents compile failures for platforms that are
part of the multi-platform kernel.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/mach-msm/Makefile

 obj-y += timer.o
-obj-y += clock.o
+obj-$(CONFIG_MSM_PROC_COMM) += clock.o
 
 obj-$(CONFIG_MSM_VIC) += irq-vic.o