hfsplus: Fix undefined __divdi3 in hfsplus_init_header_node()

ERROR: "__divdi3" [fs/hfsplus/hfsplus.ko] undefined!

Introduced by commit 099e9245 ("hfsplus: implement attributes file's
header node initialization code").

i_size_read() returns loff_t, which is long long, i.e.  64-bit.  node_size
is size_t, which is either 32-bit or 64-bit.  Hence
"i_size_read(attr_file) / node_size" is a 64-by-32 or 64-by-64 division,
causing (some versions of) gcc to emit a call to __divdi3().

Fortunately node_size is actually 16-bit, as the sole caller of
hfsplus_init_header_node() passes a u16.  Hence change its type from
size_t to u16, and use do_div() to perform a 64-by-32 division.

Not seen in m68k/allmodconfig in -next, so it really depends on the
verion of gcc.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>