scsi: atari_scsi: Fix race condition between .queuecommand and EH

It is possible that bus_reset_cleanup() or .eh_abort_handler could be
invoked during NCR5380_queuecommand(). If that takes place before the new
command is enqueued and after the ST-DMA "lock" has been acquired, the
ST-DMA "lock" will be released again. This will result in a lost DMA
interrupt and a command timeout. Fix this by excluding EH and interrupt
handlers while the new command is enqueued.

Link: https://lore.kernel.org/r/af25163257796b50bb99d4ede4025cea55787b8f.1605847196.git.fthain@telegraphics.com.au


Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>