missed mnt_drop_write() in do_dentry_open()

This one ought to be __mnt_drop_write(), to match __mnt_want_write()
in the beginning...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/open.c

@@ -717,7 +717,7 @@ static int do_dentry_open(struct file *f,
 			 * here, so just reset the state.
 			 */
 			file_reset_write(f);
-			mnt_drop_write(f->f_path.mnt);
+			__mnt_drop_write(f->f_path.mnt);
 		}
 	}
 cleanup_file: