[SCSI] aic7xxx: Test opcode, not definition in aicasm:type_check()

This fixes a bug that we treat all sequencer operations as ands and
never do the additional invalid bit checks non-and operations require
because the if () to determine this has an operand which is always
true at the end of the or statement.

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Acked-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>