IB/ehca: Fix locking for shca_list_lock

shca_list_lock is taken from softirq context in ehca_poll_eqs, so we
need to lock IRQ safe elsewhere.  Found by lockdep.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Joachim Fenkes <fenkes@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>