If the 'ptr' is a const, this code cause "assignment of read-only variable"
error on gcc 4.x.

Use __u64 instead of __typeof__(*(ptr)) for temporary variable to get
rid of errors on gcc 4.x.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>