qtnfmac: skb2rbd_attach cleanup

Update PCIE_HDP_TX_HOST_Q_WR_PTR register in skb2rbd_attach as a part of
procedure of passing new Rx buffer to hardware. Sync up all the the
qtnf_rx_bd descriptor updates before passing Rx buffer to hardware.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>