ARM: imx: add missing clk_disable_unprepare()

clock source is prepared and enabled by clk_prepare_enable()
in probe function, but no disable or unprepare in remove and
error path.

Fixes: 9454a0ca ("ARM: imx: add mmdc ipg clock operation for mmdc")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>