ncr5380: Add missing break after case MESSAGE_REJECT

MESSAGE REJECT does not imply DISCONNECT: the target is about to enter
MESSAGE IN or MESSAGE OUT phase.

This bug fix comes from atari_NCR5380.c. Unfortunately it never made it
into the original NCR5380.c core driver.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>