xfs: add missing cmap->br_state = XFS_EXT_NORM update

COW extents are already converted into written real extents after
xfs_reflink_convert_cow_locked(), therefore cmap->br_state should
reflect it.

Otherwise, there is another necessary unwritten convertion
triggered in xfs_dio_write_end_io() for direct I/O cases.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>