xfs: DAX does not use IO completion callbacks

xfs: DAX does not use IO completion callbacks

Orabug: 22913653

For DAX, we are now doing block zeroing during allocation. This
means we no longer need a special DAX fault IO completion callback
to do unwritten extent conversion. Because mmap never extends the
file size (it SEGVs the process) we don't need a callback to update
the file size, either. Hence we can remove the completion callbacks
from the __dax_fault and __dax_mkwrite calls.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
(cherry picked from commit 01a155e6cf7db1a8ff2aa73162d7d9ec05ad298f)
Signed-off-by: Dan Duval <dan.duval@oracle.com>