[S390] dcss: Initialize workqueue before using it.

In case a dcss segment cannot be loaded blk_cleanup_queue
will be called before blk_queue_make_request, leaving the
struct work unplug_work of the request queue uninitialized
before it is used.
That leads also to the lockdep message below.
To avoid that call blk_queue_make_request right after the
request_queue has been allocated.
This makes sure that the struct work is always initialized
before it is used.

INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
CPU: 2 Not tainted 2.6.24 #6
Process swapper (pid: 1, task: 000000000f854038, ksp: 000000000f85f980)
040000000f85f860 000000000f85f880 0000000000000002 0000000000000000
       000000000f85f920 000000000f85f898 000000000f85f898 000000000001622e
       0000000000000000 000000000f85f980 0000000000000000 0000000000000000
       000000000f85f880 000000000000000c 000000000f85f880 000000000f85f8f0
       0000000000342908 000000000001622e 000000000f85f880 000000000f85f8d0
Call Trace:
([<000000000001619e>] show_trace+0xda/0x104)
 [<0000000000016288>] show_stack+0xc0/0xf8
 [<00000000000163d0>] dump_stack+0xb0/0xc0
 [<000000000006e4ea>] __lock_acquire+0x47e/0x1160
 [<000000000006f27c>] lock_acquire+0xb0/0xd8
 [<000000000005a522>] __cancel_work_timer+0x9e/0x240
 [<000000000005a72e>] cancel_work_sync+0x2a/0x3c
 [<0000000000165c46>] kblockd_flush_work+0x26/0x34
 [<0000000000169034>] blk_sync_queue+0x38/0x48
 [<0000000000169080>] blk_release_queue+0x3c/0xa8
 [<000000000017bce8>] kobject_cleanup+0x58/0xac
 [<000000000017bd66>] kobject_release+0x2a/0x38
 [<000000000017d28e>] kref_put+0x6e/0x94
 [<000000000017bc80>] kobject_put+0x38/0x48
 [<00000000001653be>] blk_put_queue+0x2a/0x38
 [<0000000000168fee>] blk_cleanup_queue+0x82/0x90
 [<0000000000213e7e>] dcssblk_add_store+0x34e/0x700
 [<00000000005243b8>] dcssblk_init+0x1a0/0x308
 [<000000000050a3c2>] kernel_init+0x1b2/0x3a4
 [<000000000001ac82>] kernel_thread_starter+0x6/0xc
 [<000000000001ac7c>] kernel_thread_starter+0x0/0xc

INFO: lockdep is turned off.

Cc: Gerald Schaefer <geraldsc@de.ibm.com>
Cc: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>