[SCSI] libiscsi: avoid unnecessary multiple NULL assignments

In iscsi_free_task, NULL is assigned to task->sc twice: before and
after kfifo_in invocatoin. Allocating and freeing iscsi_task are guarded
with session->lock, so multiple NULL assignments cause no trouble. But
people reading the source code may be confused.

The second NULL assignment comes from commit:

3e5c28ad0391389959ccae81c938c7533efb3490

It seems that the line after kfifo_in invocation was introduced
accidentally.

Signed-off-by: Masatake YAMATO <[e-mail]>
Signed-off-by: Mike Christie <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/libiscsi.c

···
 	kfifo_in(&session->cmdpool.queue, (void*)&task, sizeof(void*));
 
 	if (sc) {
-		task->sc = NULL;
 		/* SCSI eh reuses commands to verify us */
 		sc->SCp.ptr = NULL;
 		/*