[SCSI] bug fix for free list handling

[SCSI] bug fix for free list handling

commit:

commit 542bd1377a963070bc4a03ff7d2690ddf3920596
Author: James Bottomley <James.Bottomley@HansenPartnership.com>
Date:   Mon Apr 21 10:57:20 2008 -0500

    [SCSI] fix SLUB WARN_ON

Fixed another problem in free list handling by moving list allocation
from scsi_host_alloc() to scsi_add_host().  Unfortunately it
introduced a new failure mode in that hosts can pass straight from
alloc to put without going through add, leaving the free list
uninitialised.

Fix by checking shost->cmd_pool on the release path to see if it got
initialised.

Signed-off-by: Alan D. Brunelle <alan.brunelle@hp.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>