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: 878d8def0603 ("libbpf: Rework feature-probing APIs")
Signed-off-by: Florian Fainelli <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/lib/bpf/libbpf_probes.c

···
 	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);