Fix MIPS64 posix_fadvise and posix_fadvise64.

Fix MIPS64 posix_fadvise and posix_fadvise64.

Similar to the problems I fixed for posix_fallocate
<http://sourceware.org/ml/libc-ports/2008-12/msg00007.html> and
fallocate <http://sourceware.org/ml/libc-ports/2009-05/msg00031.html>,
MIPS64 posix_advise also needs fixes to use the correct syscall
interfaces.  Although the existing n32 posix_fadvise64 is OK, getting
posix_fadvise from syscalls.list does not work correctly, as this
function is supposed to return an error code instead of storing it in
errno as the generic syscall implementations from syscalls.list do.