x86: ia32_signal: remove using temporary variable

Impact: cleanup

No need to use temporary variable.
Also rename the variable same as arch/x86/kernel/signal_32.c.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Reviewed-by: WANG Cong <wangcong@zeuux.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>