libosd: Use of new blk_make_request

Use new blk_make_request() to allocate a request from bio
and avoid using deprecated blk_rq_append_bio().

This patch is dependent on a block layer patch titled:
    [BLOCK] New blk_make_request() takes bio returns request

This is the last usage of blk_rq_append_bio in osd, it can now
be un-exported.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
CC: Jeff Garzik <jeff@garzik.org>
CC: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>