ARM: imx6: fix wrong fec clk

imx_get_fecclk() returns enet_ref instead of ipg.
Since the clock is used to calculate the prescaler
for the MDIO interface wrong values can be calculated.

Tested on a custom MX6S board with 100MBit interface

Signed-off-by: Markus Niebel <Markus.Niebel@tqs.de>
diff --git a/arch/arm/cpu/armv7/mx6/clock.c b/arch/arm/cpu/armv7/mx6/clock.c
index 61f71cf..bd65a08 100644
--- a/arch/arm/cpu/armv7/mx6/clock.c
+++ b/arch/arm/cpu/armv7/mx6/clock.c
@@ -409,7 +409,7 @@
 
 u32 imx_get_fecclk(void)
 {
-	return decode_pll(PLL_ENET, MXC_HCLK);
+	return mxc_get_clock(MXC_IPG_CLK);
 }
 
 static int enable_enet_pll(uint32_t en)