IB/ipath: Fix driver crash (in interrupt or during unload) after chip reset

Re-init of the kernel structures after a chip reset was leaving the
portdata structure for port zero in an inconsistent state, and a
pointer to it either stale (in re-init code) or NULL (in devdata)
Fixing the order of operations on this struct, and the condition for
interrupt access, prevents the crashes.

Signed-off-by: Bryan O'Sullivan <bryan.osullivan@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>