f2fs: remove unnecessary __init_extent_tree

[ Upstream commit 749d543c

 ]

Added into the caller.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Stable-dep-of: 043d2d00

 ("f2fs: factor out victim_entry usage from general rb_tree use")
Signed-off-by: Sasha Levin <sashal@kernel.org>