[PATCH] ia64: don't udelay() in sn_mmiob

[PATCH] ia64: don't udelay() in sn_mmiob

sn_mmiob is a lightweight way to ensure PCI write ordering, intended
to be used as an alternative to doing a PIO read. Unfortunately, with
the udelay() in there, it ends up being slower than a PCI read on
small configurations, so remove it in favor of a simple cpu_relax().