iomap: use an unsigned type for IOMAP_DIO_* defines

IOMAP_DIO_DIRTY shifts by 31 bits, which makes UBSAN unhappy. Clean up
all the defines by making the shifted value an unsigned value.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reported-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>