block: revert "bsg: setting rq->bio to NULL"

The SMP handler (sas_smp_request) was fixed to use the block API
properly, so we don't need this workaround to avoid blk_put_request()
warning.

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