erofs: simplify z_erofs_load_compact_lcluster()

erofs: simplify z_erofs_load_compact_lcluster()

[ Upstream commit 2a810ea79cd7a6d5f134ea69ca2ba726e600cbc4 ]

 - Get rid of unpack_compacted_index() and fold it into
   z_erofs_load_compact_lcluster();

 - Avoid a goto.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250114034429.431408-1-hsiangkao@linux.alibaba.com
Stable-dep-of: b44686c8391b ("erofs: fix large fragment handling")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>