IB/cm: Use spin_lock_irq() instead of spin_lock_irqsave() when possible

The ib_cm is a little over zealous about using spin_lock_irqsave,
when spin_lock_irq would do.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>