btrfs: Remove pair of bio_get/put in btrfs_schedule_bio

This code was added in 492bb6de ("Btrfs: Hold a reference on bios
during submit_bio, add some extra bio checks"). However, holding a
reference on a bio is necessary only if it's going to be referenced
after the submit_bio returns and the bio is completed. In this
particular instance this is not the case so there is no need to hold
an extra reference since we directly return.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>