x86: ia32_signal.c remove unnecessary function calls

the below 2 functions are called in save_i387_xstate_ia32()
- clear_used_math();
- stts();

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