nexus: Fix BUG() in ident_exists() on non-SMP kernel
nexus: Fix BUG() in ident_exists() on non-SMP kernel

- On at least some non-SMP kernels (e.g. 2.6.15 in Dapper), spin_is_locked()
always returns false since no locking is actually done by spin_lock().  Thus
we can't use spin_is_locked() in a BUG_ON() test as we currently do in
ident_exists().  Remove the test.

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr