wlcore: fix occasional AP TX stop after recovery

The fw_status wasn't zeroed during allocation, this caused to
occasional AP traffic stops after recovery. The wrong value in
the "wl->fw_status_2->counters.tx_lnk_free_pkts" led to a bad
"lnk->allocated_pkts" calculation in the wlcore_fw_status()
causing the wl18xx_lnk_low_prio() to return FALSE
(lnk->allocated_pkts > thold).
This eventually blocked the link in the wlcore_tx_work_locked()
as the wl1271_skb_dequeue() continuously return NULL.

Fix this by zeroing the wl->fw_status_1/2 during allocation.

Signed-off-by: Victor Goldenshtein <victorg@ti.com>