libbpf: Initialize err in probe_map_create

GCC-11 warns about the possibly unitialized err variable in
probe_map_create:

libbpf_probes.c: In function 'probe_map_create':
libbpf_probes.c:361:38: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  361 |                 return fd < 0 && err == exp_err ? 1 : 0;
      |                                  ~~~~^~~~~~~~~~

Fixes: 878d8def ("libbpf: Rework feature-probing APIs")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20220801025109.1206633-1-f.fainelli@gmail.com

tools/lib/bpf/libbpf_probes.c

@@ -193,7 +193,7 @@ static int probe_map_create(enum bpf_map_type map_type)
 	LIBBPF_OPTS(bpf_map_create_opts, opts);
 	int key_size, value_size, max_entries;
 	__u32 btf_key_type_id = 0, btf_value_type_id = 0;
-	int fd = -1, btf_fd = -1, fd_inner = -1, exp_err = 0, err;
+	int fd = -1, btf_fd = -1, fd_inner = -1, exp_err = 0, err = 0;
 
 	key_size	= sizeof(__u32);
 	value_size	= sizeof(__u32);