x86, UV: Fix initialization of max_pnode

Fix calculation of "max_pnode" for systems where the the highest
blade has neither cpus or memory. (And, yes, although rare this
does occur).

Signed-off-by: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20100910150808.GA19802@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>