staging: wfx: correctly retrieve vif ID from Tx confirmation

staging: wfx: correctly retrieve vif ID from Tx confirmation

The device is able to send multiple Tx confirmations in the one reply.
In this case, there is only one vif identifier for all the
confirmations.

Unfortunately, to generate this kind of messages the device squashes all
the confirmations whatever their vif ID and use the vif ID of the first
confirmation. So, the driver cannot rely on the vif ID mentioned in the
header. Fortunately, using the packet_id, the driver can retrieve the Tx
request and the associated vif.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200701150707.222985-4-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>