user_regset_copyout_zero(): use clear_user()

that's the only caller of __clear_user() in generic code, and it's
not hot enough to bother with skipping access_ok().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/regset.h

@@ -320,7 +320,7 @@ static inline int user_regset_copyout_zero(unsigned int *pos,
 		if (*kbuf) {
 			memset(*kbuf, 0, copy);
 			*kbuf += copy;
-		} else if (__clear_user(*ubuf, copy))
+		} else if (clear_user(*ubuf, copy))
 			return -EFAULT;
 		else
 			*ubuf += copy;