[SCSI] Fix thread termination for the SCSI error handle

From: 	Alan Stern <stern@rowland.harvard.edu>

This patch (as561) fixes the error handler's thread-exit code.  The
kthread_stop call won't wake the thread from a down_interruptible, so
the patch gets rid of the semaphore and simply does

        set_current_state(TASK_INTERRUPTIBLE);

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Modified to simplify the termination loop and correct the sleep condition.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>