[SCSI] qla2xxx: don't free pool that wasn't allocated

In the original code, if dma_pool_alloc() fails then we call
dma_pool_free().  It causes an error, possibly a NULL dereference.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>