[PATCH] powerpc: Fix mmap returning 64 bit addresses

The merge of syscalls.c & sys_ppc32.c (30286ef6)
broke mmap, if the mmap returned a 64 bit address.

do_mmap2 was taking the return value from do_mmap_pgoff (an unsigned long), and
storing it in an int, before returning it to sys_mmap as an unsigned long. So
we were losing the high bits of the address.

You would have thought the compiler could catch this for us ...

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>