vfs: add file_path() helper

Turn
	d_path(&file->f_path, ...);
into
	file_path(file, ...);

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 2bc56e2..dda33d6 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -834,7 +834,7 @@
 		if (bitmap->storage.file) {
 			path = kmalloc(PAGE_SIZE, GFP_KERNEL);
 			if (path)
-				ptr = d_path(&bitmap->storage.file->f_path,
+				ptr = file_path(bitmap->storage.file,
 					     path, PAGE_SIZE);
 
 			printk(KERN_ALERT