[SCSI] aic79xx: fix sense_buffer access bug

The commit de25deb1

 changed
scsi_cmnd.sense_buffer from a static array to a dynamically allocated
buffer. We can't access to sense_buffer in '&cmd->sense_buffer' way.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>