bpf: Fix passing zero to PTR_ERR() in bpf_btf_printf_prepare

There is a bug when passing zero to PTR_ERR() and return.
Fix the smatch error.

Fixes: c4d0bfb ("bpf: Add bpf_snprintf_btf helper")
Signed-off-by: Wang Qing <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Acked-by: John Fastabend <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: Wang Qing

kernel/trace/bpf_trace.c

@@ -1198,7 +1198,7 @@ static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
 	*btf = bpf_get_btf_vmlinux();
 
 	if (IS_ERR_OR_NULL(*btf))
-		return PTR_ERR(*btf);
+		return IS_ERR(*btf) ? PTR_ERR(*btf) : -EINVAL;
 
 	if (ptr->type_id > 0)
 		*btf_id = ptr->type_id;