iomap: free the bio before completing the dio

iomap: free the bio before completing the dio

There are good arguments for processing the user completions ASAP vs.
freeing resources ASAP, but freeing the bio first here removes potential
use after free hazards when checking flags, and will simplify the
upcoming bounce buffer support.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Tested-by: Anuj Gupta <anuj20.g@samsung.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>