propagate error from get_empty_filp() to its callers

Based on parts from Anatol's patch (the rest is the next commit).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index df00b75..e0a33f5 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2941,8 +2941,8 @@
 	int error;
 
 	file = get_empty_filp();
-	if (!file)
-		return ERR_PTR(-ENFILE);
+	if (IS_ERR(file))
+		return file;
 
 	file->f_flags = op->open_flag;