bpf: Suppress 'passing zero to PTR_ERR' warning

Kernel Test Robot complains about passing zero to PTR_ERR for the said
line, suppress it by using PTR_ERR_OR_ZERO.

Fixes: c0a5a21 ("bpf: Allow storing referenced kptr in map")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220521132620.1976921-1-memxor@gmail.com

Author: kkdwvd

kernel/bpf/verifier.c

@@ -5352,7 +5352,7 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
 		return -EINVAL;
 	}
 	if (!map_value_has_kptrs(map_ptr)) {
-		ret = PTR_ERR(map_ptr->kptr_off_tab);
+		ret = PTR_ERR_OR_ZERO(map_ptr->kptr_off_tab);
 		if (ret == -E2BIG)
 			verbose(env, "map '%s' has more than %d kptr\n", map_ptr->name,
 				BPF_MAP_VALUE_OFF_MAX);