Chuck Ebbert noticed that the desc_empty macro is incorrect.  Fix it.

Thankfully, this is not used as a security check, but it can falsely
overwrite TLS segments with carefully chosen base / limits.  I do not
believe this is an issue in practice, but it is a kernel bug.
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Chris Wright <chrisw@osdl.org>

[ x86-64 had the same problem, and the same fix. Linus ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>