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/mm/memory.c b/mm/memory.c
index 22e037e..28c10da 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3724,7 +3724,7 @@
 		if (buf) {
 			char *p;
 
-			p = d_path(&f->f_path, buf, PAGE_SIZE);
+			p = file_path(f, buf, PAGE_SIZE);
 			if (IS_ERR(p))
 				p = "?";
 			printk("%s%s[%lx+%lx]", prefix, kbasename(p),