x86: ia32_signal: cleanup macro RELOAD_SEG

Impact: cleanup

Remove mask parameter because it's always 3.
Cleanup coding styles.

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>