afs: Fix an IS_ERR() vs NULL check

The proc_symlink() function returns NULL on error, it doesn't return
error pointers.

Fixes: 5b86d4ff ("afs: Implement network namespacing")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/YLjMRKX40pTrJvgf@mwanda/Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/afs/main.c

@@ -203,8 +203,8 @@ static int __init afs_init(void)
 		goto error_fs;
 
 	afs_proc_symlink = proc_symlink("fs/afs", NULL, "../self/net/afs");
-	if (IS_ERR(afs_proc_symlink)) {
-		ret = PTR_ERR(afs_proc_symlink);
+	if (!afs_proc_symlink) {
+		ret = -ENOMEM;
 		goto error_proc;
 	}