x86: change_page_attr_clear fix

This patch replaces __change_page_attr_set_clr() with
change_page_attr_set_clr() in change_page_attr_clear() to flush the
TLB/cache properly.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>