x86: ia32_signal: change order of storing in setup_sigcontext()

Impact: cleanup

Change order of storing to match the sigcontext_ia32.
And add casting to make this code same as arch/x86/kernel/signal_32.c.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>