libbpf: fix warning that PTR_ERR_OR_ZERO can be used

Fix below warning reported by coccicheck:

/tools/lib/bpf/libbpf.c:3461:1-3: WARNING: PTR_ERR_OR_ZERO can be used
Signed-off-by: NHariprasad Kelam <hariprasad.kelam@gmail.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/libbpf.c

@@ -3460,9 +3460,7 @@ bpf_object__find_map_by_offset(struct bpf_object *obj, size_t offset)
 
 long libbpf_get_error(const void *ptr)
 {
-	if (IS_ERR(ptr))
-		return PTR_ERR(ptr);
-	return 0;
+	return PTR_ERR_OR_ZERO(ptr);
 }
 
 int bpf_prog_load(const char *file, enum bpf_prog_type type,