x86, xsave: remove the redundant access_ok() in setup_rt_frame()

save_i387_xstate() is already doing the required access_ok(). Remove
the redundant access_ok() before it.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>