use the simpler spin_trylock_irqsave() API to get the adapter lock.

[ this is also a fix for -rt where adapter->lock is a sleeping lock. ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jay Cliburn <jacliburn@bellsouth.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>