libbpf: Fix uninitialized variable in btf_parse_type_sec

Fix obvious unitialized variable use that wasn't reported by compiler. libbpf
Makefile changes to catch such errors are added separately.

Fixes: 3289959b ("libbpf: Support BTF loading and raw data output in both endianness")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200929220604.833631-1-andriin@fb.com

tools/lib/bpf/btf.c

@@ -347,7 +347,7 @@ static int btf_parse_type_sec(struct btf *btf)
 	struct btf_header *hdr = btf->hdr;
 	void *next_type = btf->types_data;
 	void *end_type = next_type + hdr->type_len;
-	int err, i, type_size;
+	int err, i = 0, type_size;
 
 	/* VOID (type_id == 0) is specially handled by btf__get_type_by_id(),
 	 * so ensure we can never properly use its offset from index by