btrfs: scrub: remove unused btrfs_path in scrub_simple_mirror()

The @path in scrub_simple_mirror() is no longer utilized after commit
e02ee89b ("btrfs: scrub: switch scrub_simple_mirror() to scrub_stripe
infrastructure").

Before that commit, we call find_first_extent_item() directly, which
needs a path and that path can be reused.  But after that switch commit,
the extent search is done inside queue_scrub_stripe(), which will no
longer accept a path from outside.

So the @path variable can be safely removed.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ remove the stale comment ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/scrub.c

@@ -1957,16 +1957,12 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
 {
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
 	const u64 logical_end = logical_start + logical_length;
-	/* An artificial limit, inherit from old scrub behavior */
-	struct btrfs_path path = { 0 };
 	u64 cur_logical = logical_start;
 	int ret;
 
 	/* The range must be inside the bg */
 	ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);
 
-	path.search_commit_root = 1;
-	path.skip_locking = 1;
 	/* Go through each extent items inside the logical range */
 	while (cur_logical < logical_end) {
 		u64 cur_physical = physical + cur_logical - logical_start;
@@ -2010,7 +2006,6 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
 		/* Don't hold CPU for too long time */
 		cond_resched();
 	}
-	btrfs_release_path(&path);
 	return ret;
 }