iomap: don't bother unsharing delalloc extents

[ Upstream commit f7a4874d ]

If unshare encounters a delalloc reservation in the srcmap, that means
that the file range isn't shared because delalloc reservations cannot be
reflinked.  Therefore, don't try to unshare them.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20241002150040.GB21853@frogsfrogsfrogs


Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Stable-dep-of: 50793801 ("fsdax: dax_unshare_iter needs to copy entire blocks")
Signed-off-by: Sasha Levin <sashal@kernel.org>