ncr5380: Fix wait for 53C80 registers registers after PDMA

The check for 53C80 registers accessibility was commented out because
it was broken (inverted). Fix and enable it.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
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>