compat: sync compat_stats with statfs.

This was found by inspection while tracking a similar
bug in compat_statfs64, that has been fixed in mainline
since decemeber.

- This fixes a bug where not all of the f_spare fields
  were cleared on mips and s390.
- Add the f_flags field to struct compat_statfs
- Copy f_flags to userspace in case someone cares.
- Use __clear_user to copy the f_spare field to userspace
  to ensure that all of the elements of f_spare are cleared.
  On some architectures f_spare is has 5 ints and on some
  architectures f_spare only has 4 ints.  Which makes
  the previous technique of clearing each int individually
  broken.

I don't expect anyone actually uses the old statfs system
call anymore but if they do let them benefit from having
the compat and the native version working the same.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

arch/mips/include/asm/compat.h

@@ -111,7 +111,8 @@ struct compat_statfs {
 	int		f_bavail;
 	compat_fsid_t	f_fsid;
 	int		f_namelen;
-	int		f_spare[6];
+	int		f_flags;
+	int		f_spare[5];
 };
 
 #define COMPAT_RLIM_INFINITY	0x7fffffffUL