bcachefs: Fix some spurious gcc warnings

These only come up when building in userspace, for some reason.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_key_cache.c

@@ -317,7 +317,7 @@ static int btree_key_cache_flush_pos(struct btree_trans *trans,
 	struct bch_fs *c = trans->c;
 	struct journal *j = &c->journal;
 	struct btree_iter *c_iter = NULL, *b_iter = NULL;
-	struct bkey_cached *ck;
+	struct bkey_cached *ck = NULL;
 	int ret;
 
 	b_iter = bch2_trans_get_iter(trans, key.btree_id, key.pos,

fs/bcachefs/movinggc.c

@@ -61,7 +61,7 @@ static enum data_cmd copygc_pred(struct bch_fs *c, void *arg,
 	copygc_heap *h = &c->copygc_heap;
 	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
 	const union bch_extent_entry *entry;
-	struct extent_ptr_decoded p;
+	struct extent_ptr_decoded p = { 0 };
 
 	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
 		struct bch_dev *ca = bch_dev_bkey_exists(c, p.ptr.dev);