selftests/bpf: fix compiler warnings in RELEASE=1 mode

When compiling BPF selftests with RELEASE=1, we get two new
warnings, which are treated as errors. Fix them.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20231212225343.1723081-1-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/veristat.c

@@ -1254,7 +1254,7 @@ static int cmp_join_stat(const struct verif_stats_join *s1,
 			 bool asc, bool abs)
 {
 	const char *str1 = NULL, *str2 = NULL;
-	double v1, v2;
+	double v1 = 0.0, v2 = 0.0;
 	int cmp = 0;
 
 	fetch_join_stat_value(s1, id, var, &str1, &v1);

tools/testing/selftests/bpf/xdp_hw_metadata.c

@@ -79,7 +79,7 @@ static int open_xsk(int ifindex, struct xsk *xsk, __u32 queue_id)
 		.flags = XSK_UMEM__DEFAULT_FLAGS,
 		.tx_metadata_len = sizeof(struct xsk_tx_metadata),
 	};
-	__u32 idx;
+	__u32 idx = 0;
 	u64 addr;
 	int ret;
 	int i;