interconnect: debugfs: initialize src_node and dst_node to empty strings

interconnect: debugfs: initialize src_node and dst_node to empty strings

The debugfs_create_str() API assumes that the string pointer is either NULL
or points to valid kmalloc() memory. Leaving the pointer uninitialized can
cause problems.

Initialize src_node and dst_node to empty strings before creating the
debugfs entries to guarantee that reads and writes are safe.

Fixes: 770c69f037c1 ("interconnect: Add debugfs test client")
Signed-off-by: Georgi Djakov <djakov@kernel.org>
Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Tested-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Link: https://lore.kernel.org/r/20260109122523.125843-1-djakov@kernel.org
Signed-off-by: Georgi Djakov <djakov@kernel.org>