omap: i2c: Avoid compilation error in case the header is included multiple times

Added defines to avoid compilation error.
Signed-off-by: Subramaniam C.A <subramaniam.ca@ti.com>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/plat-omap/include/plat/i2c.h

@@ -18,6 +18,8 @@
  * 02110-1301 USA
  *
  */
+#ifndef __ASM__ARCH_OMAP_I2C_H
+#define __ASM__ARCH_OMAP_I2C_H
 
 #include <linux/i2c.h>
 
@@ -36,3 +38,5 @@ static inline int omap_register_i2c_bus(int bus_id, u32 clkrate,
 
 void __init omap1_i2c_mux_pins(int bus_id);
 void __init omap2_i2c_mux_pins(int bus_id);
+
+#endif /* __ASM__ARCH_OMAP_I2C_H */