btrfs: remove unnecessary NULL pointer checks when searching extent maps

The previous and next pointer arguments passed to __tree_search() are
never NULL as the only caller of this function, __lookup_extent_mapping(),
always passes the address of two on stack pointers. So remove the NULL
checks and add assertions to verify the pointers.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_map.c

@@ -150,6 +150,9 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 	struct extent_map *entry;
 	struct extent_map *prev_entry = NULL;
 
+	ASSERT(prev_ret);
+	ASSERT(next_ret);
+
 	while (n) {
 		entry = rb_entry(n, struct extent_map, rb_node);
 		prev = n;
@@ -163,7 +166,6 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 			return n;
 	}
 
-	if (prev_ret) {
 	orig_prev = prev;
 	while (prev && offset >= extent_map_end(prev_entry)) {
 		prev = rb_next(prev);
@@ -171,16 +173,14 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 	}
 	*prev_ret = prev;
 	prev = orig_prev;
-	}
 
-	if (next_ret) {
 	prev_entry = rb_entry(prev, struct extent_map, rb_node);
 	while (prev && offset < prev_entry->start) {
 		prev = rb_prev(prev);
 		prev_entry = rb_entry(prev, struct extent_map, rb_node);
 	}
 	*next_ret = prev;
-	}
+
 	return NULL;
 }