ath10k: add per target config of max_num_peers

This patch makes sure the value of max_num_peers matches
num_peers in hw_params (if set to a non zero value).

hw_params->num_peers is used in the TLV WMI init command.
If ar->max_num_peers is not set to the same value, there is a risk
that the user creates more peers than the maximum number of peers
supported by the device.

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