libbpf: Fix the possible memory leak on error

If the strdup() fails then we need to call bpf_object__close(obj) to
avoid a resource leak.

Fixes: 166750bc ("libbpf: Support libbpf-provided extern variables")
Signed-off-by: Shuyi Cheng <chengshuyi@linux.alibaba.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1626180159-112996-3-git-send-email-chengshuyi@linux.alibaba.com

tools/lib/bpf/libbpf.c

@@ -7649,8 +7649,10 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 	kconfig = OPTS_GET(opts, kconfig, NULL);
 	if (kconfig) {
 		obj->kconfig = strdup(kconfig);
-		if (!obj->kconfig)
-			return ERR_PTR(-ENOMEM);
+		if (!obj->kconfig) {
+			err = -ENOMEM;
+			goto out;
+		}
 	}
 
 	err = bpf_object__elf_init(obj);