DaVinci: fix compilation warnings in <mach/clkdev.h>

Commit 6d803ba7 (ARM: 6483/1: arm & sh:
factorised duplicated clkdev.c) caused the following warnings:

In file included from /home/headless/src/kernel.org/linux-davinci/arch/arm/
include/asm/clkdev.h:17,
                 from include/linux/clkdev.h:15,
                 from arch/arm/mach-davinci/clock.h:71,
                 from arch/arm/mach-davinci/common.c:22:
arch/arm/mach-davinci/include/mach/clkdev.h:4: warning: `struct clk' declared
inside parameter list
arch/arm/mach-davinci/include/mach/clkdev.h:4: warning: its scope is only this
definition or declaration, which is probably not what you want
arch/arm/mach-davinci/include/mach/clkdev.h:9: warning: `struct clk' declared
inside parameter list
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>

arch/arm/mach-davinci/include/mach/clkdev.h

 #ifndef __MACH_CLKDEV_H
 #define __MACH_CLKDEV_H
 
+struct clk;
+
 static inline int __clk_get(struct clk *clk)
 {
 	return 1;