nsfs: clean-up ns_get_path() signature to return int

ns_get_path() and ns_get_path_cb() only ever return either NULL or an
ERR_PTR. It is far more idiomatic to simply return an integer, and it
makes all of the callers of ns_get_path() more straightforward to read.

Fixes: e149ed2b80 ("take the targets of /proc/*/ns/* symlinks to separate fs")
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/events/core.c

@@ -7495,7 +7495,7 @@ static void perf_fill_ns_link_info(struct perf_ns_link_info *ns_link_info,
 {
 	struct path ns_path;
 	struct inode *ns_inode;
-	void *error;
+	int error;
 
 	error = ns_get_path(&ns_path, task, ns_ops);
 	if (!error) {