[SCSI] aic7xxx_old, eata_pio, ips, libsas: don't zero out sense_buffer in queuecommand

LLDs don't need to zero out scsi_cmnd::sense_buffer in queuecommand
since scsi-ml does. This is a preparation of the future changes to
allocate the sense_buffer only when necessary.

Many LLDs zero out the sense_buffer before touching it on the error
case. This patch lets them alone for now because new APIs for them
would be added later on.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: "Salyzyn, Mark" <Mark_Salyzyn@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>