soc: imx8m: don't access of_root directly

soc: imx8m: don't access of_root directly

Don't access of_root directly as it reduces the build test coverage for
this driver with COMPILE_TEST=y and OF=n. Use existing helper functions
to retrieve the relevant information.

Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260223-soc-of-root-v2-6-b45da45903c8@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>