Use devm_of_iomap() instead of of_iomap() to automatically handle
the unused ioremap region.

If any error occurs, regions allocated by kzalloc() will leak,
but using devm_kzalloc() instead will automatically free the memory
using devm_kfree().

Fixes: daeb1454 ("clk: imx: imx8mn: Switch to clk_hw based API")
Fixes: 96d6392b ("clk: imx: Add support for i.MX8MN clock driver")
Signed-off-by: Hao Luo <m202171776@hust.edu.cn>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20230411015107.2645-1-m202171776@hust.edu.cnSigned-off-by: Abel Vesa <abel.vesa@linaro.org>