[PATCH] x86-64: Fix (harmless) typo in head.S early level2 page table

The global bit  was not set in the first 2MB page, instead
it had a bit in the free AVL section which is useless.
Fixed thus.

Noticed by Eric Biederman

Cc:  Eric W. Biederman <ebiederm@xmission.com>

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>