block, fs, mm, drivers: use bio set/get op accessors

This patch converts the simple bi_rw use cases in the block,
drivers, mm and fs code to set/get the bio operation using
bio_set_op_attrs/bio_op

These should be simple one or two liner cases, so I just did them
in one patch. The next patches handle the more complicated
cases in a module per patch.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

mm/page_io.c

@@ -317,7 +317,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		ret = -ENOMEM;
 		goto out;
 	}
-	bio->bi_rw = WRITE;
+	bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
 	if (wbc->sync_mode == WB_SYNC_ALL)
 		bio->bi_rw |= REQ_SYNC;
 	count_vm_event(PSWPOUT);
@@ -370,7 +370,7 @@ int swap_readpage(struct page *page)
 		ret = -ENOMEM;
 		goto out;
 	}
-	bio->bi_rw = READ;
+	bio_set_op_attrs(bio, REQ_OP_READ, 0);
 	count_vm_event(PSWPIN);
 	submit_bio(bio);
 out: