scsi: aic94xx: Add a missing call to kfree

Most error branches following the call to kzalloc contain a call to
kfree. This patch add these calls where they are missing and set the
relevant pointers to NULL.

This issue was found with Hector.

Signed-off-by: Quentin Lambert <lambert.quentin@gmail.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>