dmx3191d: Drop max_sectors limit

The dmx3191d driver is not capable of DMA or PDMA so all transfers
use PIO. Now that large slow PIO transfers periodically stop and call
cond_resched(), the max_sectors limit can go away.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>