x86, xsave: Cleanup return codes in check_for_xstate()

The places which call check_for_xstate() only care about zero or
non-zero so this patch doesn't change how the code runs, but it's a
cleanup.  The main reason for this patch is that I'm looking for places
which don't return -EFAULT for copy_from_user() failures.

Signed-off-by: Dan Carpenter <error27@gmail.com>
LKML-Reference: <20100603100746.GU5483@bicker>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>