f2fs: remove struct segment_allocation default_salloc_ops

f2fs: remove struct segment_allocation default_salloc_ops

[ Upstream commit 1c8a8ec0a0e9a1176022a35c4daf04fe1594d270 ]

There is only  single instance of these ops, so remove the indirection
and call allocate_segment_by_default directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Stable-dep-of: 43563069e1c1 ("f2fs: check curseg->inited before write_sum_page in change_curseg")
Signed-off-by: Sasha Levin <sashal@kernel.org>