[PATCH] x86_64: serialize assign_irq_vector() use of static variables

Since assign_irq_vector() can be called at runtime, its access of static
variables should be protected by a lock.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>