[SCSI] fix intermittent oops in scsi_bus_uevent

Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>
> BUG: unable to handle kernel paging request at e6f17fac
> IP: [<c02604d6>] scsi_bus_uevent+0x1/0x17
> *pde = 2714b163 *pte = 26f17160
> Oops: 0000 [#1] DEBUG_PAGEALLOC
> last sysfs file:
>
> Pid:  1, comm: swapper Not tainted (2.6.26-rc2-next-20080516skw #30)
> EIP: 0060:[<c02604d6>] EFLAGS: 00010282 CPU: 0
> EIP is at scsi_bus_uevent+0x1/0x17
> EAX: e6f18014 EBX: e6f18014 ECX: c02604d5 EDX: e7173000
> ESI: e7173000 EDI: e7173000 EBP: e7851ca0 ESP: e7851c90
>  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068

The problem is caused by:

commit b0ed4336


Author: Hannes Reinecke <hare@suse.de>
Date:   Tue Mar 18 14:32:28 2008 +0100

    [SCSI] add scsi_host and scsi_target to scsi_bus

which added scsi_bus_type to the struct scsi_target device.  This
causes both the scsi_device and scsi_target to fire scsi_bus_uevents.
However, the actualy scsi_bus_uevent() call assumes blindly that it's
a struct scsi_device.  Check for this and return immediately if it
isn't.

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