qtnfmac: fix releasing Tx/Rx data buffers

Add missing PCI unmap for Tx buffers and release all buffers explicitly.
Managed release using devm_add_action is not suitable for qtnfmac Tx/Rx
data buffers. The reason is in ordering and dependencies: buffers
should be released after transmission is stopped but before PCI
device resources and DMA allocations are released.

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