The sgl is freed in the target stack in target_release_cmd_kref() before
calling qlt_free_cmd() but there is an unmap of sgl in qlt_free_cmd() that
causes a panic if sgl is not yet DMA unmapped:

NIP dma_direct_unmap_sg+0xdc/0x180
LR  dma_direct_unmap_sg+0xc8/0x180
Call Trace:
 ql_dbg_prefix+0x68/0xc0 [qla2xxx] (unreliable)
 dma_unmap_sg_attrs+0x54/0xf0
 qlt_unmap_sg.part.19+0x54/0x1c0 [qla2xxx]
 qlt_free_cmd+0x124/0x1d0 [qla2xxx]
 tcm_qla2xxx_release_cmd+0x4c/0xa0 [tcm_qla2xxx]
 target_put_sess_cmd+0x198/0x370 [target_core_mod]
 transport_generic_free_cmd+0x6c/0x1b0 [target_core_mod]
 tcm_qla2xxx_complete_free+0x6c/0x90 [tcm_qla2xxx]

The sgl may be left unmapped in error cases of response sending.  For
instance, qlt_rdy_to_xfer() maps sgl and exits when session is being
deleted keeping the sgl mapped.

This patch removes use-after-free of the sgl and ensures that the sgl is
unmapped for any command that was not sent to firmware.

Link: https://lore.kernel.org/r/20211018122650.11846-1-d.bogdanov@yadro.comReviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>