hfsplus: fix compiler warning on PowerPC

Commit a99b7069 ("hfsplus: Fix undefined __divdi3 in
hfsplus_init_header_node()") introduced do_div() to xattr.c and the
warning below too.

As Geert remarked: "tmp" is "loff_t" which is "__kernel_loff_t", which
is "long long", i.e.  signed, while include/asm-generic/div64.h compares
its type with "uint64_t".  As inode sizes are positive, it should be
safe to change the type of "tmp" to "u64".

  In file included from
  arch/powerpc/include/asm/div64.h:1:0,
                    from include/linux/kernel.h:124,
                    from include/asm-generic/bug.h:13,
                    from arch/powerpc/include/asm/bug.h:127,
                    from include/linux/bug.h:4,
                    from include/linux/thread_info.h:11,
                    from include/asm-generic/preempt.h:4,
                    from arch/powerpc/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:18,
                    from include/linux/spinlock.h:50,
                    from include/linux/wait.h:8,
                    from include/linux/fs.h:6,
                    from fs/hfsplus/hfsplus_fs.h:19,
                    from fs/hfsplus/xattr.c:9:
  fs/hfsplus/xattr.c: In function 'hfsplus_init_header_node':
  include/asm-generic/div64.h:43:28: warning: comparison of distinct pointer types lacks a cast [enabled by default]
     (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
                               ^
  fs/hfsplus/xattr.c:86:2: note: in expansion of macro 'do_div'
     do_div(tmp, node_size);
     ^

Signed-off-by: Christian Kujau <lists@nerdbynature.de>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Sergei Antonov <saproj@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>