IPoIB/cm: spin_lock_irqsave() -> spin_lock_irq() replacements

There are quite a few places in ipoib_cm.c where we know IRQs are
enabled because we do something that sleeps in the same function, so
we can convert several occurrences of spin_lock_irqsave() to a plain
spin_lock_irq().  This cleans up the source a little and makes the
code smaller too:

add/remove: 0/0 grow/shrink: 1/5 up/down: 3/-51 (-48)
function                                     old     new   delta
ipoib_cm_tx_reap                             403     406      +3
ipoib_cm_stale_task                          146     145      -1
ipoib_cm_dev_stop                            173     172      -1
ipoib_cm_tx_handler                          964     956      -8
ipoib_cm_rx_handler                          956     937     -19
ipoib_cm_skb_reap                            212     190     -22

Signed-off-by: Roland Dreier <rolandd@cisco.com>