staging: wfx: fix rate control handling

A tx_retry_policy (the equivalent of a list of ieee80211_tx_rate in
hardware API) is not able to include a rate multiple time. So currently,
the driver merges the identical rates from the policy provided by
minstrel (and it try to do the best choice it can in the associated
flags) before to sent it to firmware.

Until now, when rates are merged, field "count" is set to
max(count1, count2). But, it means that the sum of retries for all rates
could be far less than initial number of retries. So, this patch changes
the value of field "count" to count1 + count2. Thus, sum of all retries
for all rates stay the same.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191217161318.31402-7-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>