Move the code that retries requests from scsi_dma_restart_bh() to its own,
non-static, function. This will allow us to call it from the
retry_request_cb() of scsi-disk in a future patch.
Signed-off-by: Jiahui Cen <cenjiahui(a)huawei.com>
Signed-off-by: Ying Fang <fangying1(a)huawei.com>
