[SCSI] 3w-xxxx: remove unnecessary local_irq_save/restore for scsi sg copy API

Since the commit 50bed2e2 (sg: disable
interrupts inside sg_copy_buffer), no need to disable interrupts
before calling scsi_sg_copy_from_buffer. So we can simplify
tw_transfer_internal, which disables interrupts just for
scsi_sg_copy_from_buffer.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp&gt;\>
Acked-by: Adam Radford <linuxraid@amcc.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>