drivers/of: fdt: validate stdout-path properties before parsing them

drivers/of: fdt: validate stdout-path properties before parsing them

early_init_dt_scan_chosen_stdout() fetches stdout-path and
linux,stdout-path directly from the flat DT and immediately passes the
result to strchrnul(). Flat DT properties are raw firmware-supplied
byte sequences, and this path does not prove that either property is
NUL-terminated within its declared bounds.

Use fdt_stringlist_get() so malformed unterminated stdout-path
properties are rejected before the local parser walks them as C
strings.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260403143001.1-dt-fdt-stdout-pengpeng@iscas.ac.cn
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>