interconnect: debugfs: fix devm_kstrdup and kfree mismatch

interconnect: debugfs: fix devm_kstrdup and kfree mismatch

debugfs_write_file_str() uses standard kfree() to release old strings.
Initializing src_node and dst_node with devm_kstrdup() creates a memory
management mismatch. If a user writes to these debugfs nodes, the
devm-allocated memory is freed via kfree(), leaving a dangling pointer
in the device resource list that can lead to a double free.

Fix this by using standard kstrdup() instead. Since the interconnect
subsystem is strictly built-in and cannot be unloaded as a module, there
is no exit path requiring manual cleanup of these strings. The error
handling path is also simplified by taking advantage of the fact that
kfree(NULL) is a safe no-op.

Fixes: 8cc27f5c6dd1 ("interconnect: debugfs: initialize src_node and dst_node to empty strings")
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Link: https://msgid.link/20260318024815.7655-1-hanguidong02@gmail.com
Signed-off-by: Georgi Djakov <djakov@kernel.org>