imx6: clk: Gate off ENFC clock before setting clock rate
This fixes NAND initialization issue which appears occasionally on
some i.MX6 SoCs (particulary was observed on phyCARD-i.MX6 with
i.MX6Solo).
Signed-off-by: Dmitry Lavnikevich <d.lavnikevich@sam-solutions.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>