btrfs: update __btrfs_map_block for REQ_OP transition

We no longer pass in a bitmap of rq_flag_bits bits to __btrfs_map_block.
It will always be a REQ_OP, or the btrfs specific REQ_GET_READ_MIRRORS,
so this drops the bit tests.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 689d25a..5796c4a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2048,7 +2048,7 @@
 	 */
 	btrfs_bio_counter_inc_blocked(root->fs_info);
 	/* Tell the block device(s) that the sectors can be discarded */
-	ret = btrfs_map_block(root->fs_info, REQ_DISCARD,
+	ret = btrfs_map_block(root->fs_info, REQ_OP_DISCARD,
 			      bytenr, &num_bytes, &bbio, 0);
 	/* Error condition is -ENOMEM */
 	if (!ret) {