Add "imx_get_i2cclk" for MX51

[Alexander Shiyan]

--- barebox-v2011.09.0.orig/arch/arm/mach-imx/speed-imx51.c	2011-08-26 18:23:46.000000000 +0400
+++ barebox-v2011.09.0/arch/arm/mach-imx/speed-imx51.c	2011-09-02 15:06:17.000000000 +0400
@@ -156,6 +156,11 @@
 	return imx_get_ipgclk();
 }

+unsigned long imx_get_i2cclk(void)
+{
+	return imx_get_ipgclk();
+}
+
 unsigned long imx_get_mmcclk(void)
 {
 	u32 reg, prediv, podf, rate;