scsi: NCR5380: Reduce NCR5380_maybe_release_dma_irq() call sites

Refactor to avoid needless calls to NCR5380_maybe_release_dma_irq().
This makes the machine code smaller and the source more readable.

Link: https://lore.kernel.org/r/c1317ae8fdcb498460de5d7ea0bd62a42f5eeca8.1605847196.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>