ath10k: add default value for num_peers in WMI TLV init

The hw_params value will only be used if it was explicitly set in the
global hw_params array.

This makes it possible to have the num_peers member unset.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>