scsi: zorro_esp: Limit DMA transfers to 65535 bytes

The core driver, esp_scsi, does not use the ESP_CONFIG2_FENAB bit, so the
chip's Transfer Counter register is only 16 bits wide (not 24).  A larger
transfer cannot work and will theoretically result in a failed command
and a "DMA length is zero" error.

Fixes: 3109e5ae

 ("scsi: zorro_esp: New driver for Amiga Zorro NCR53C9x boards")
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Cc: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>