clk: imx: clk-imx8mn: fix memory leak in imx8mn_clocks_probe

In the Linux kernel, the following vulnerability has been resolved:

clk: imx: clk-imx8mn: fix memory leak in imx8mn_clocks_probe

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().