ASoC: SOF: ipc4-topology: Use size_add() in call to struct_size()

If, for any reason, the open-coded arithmetic causes a wraparound,
the protection that `struct_size()` adds against potential integer
overflows is defeated. Fix this by hardening call to `struct_size()`
with `size_add()`.

Fixes: f9efae95

 ("ASoC: SOF: ipc4-topology: Add support for base config extension")
Signed-off-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/ZQSr15AYJpDpipg6@work


Signed-off-by: Mark Brown <broonie@kernel.org>