brcm80211: fmac: use counters in brcmf_bus structure

The usb code defines a structure for counting statistics. However,
it should use the statistics entry provided in brcmf_bus as that is
exposed to the net_device. The usb private statistics counter only
remains with counters for control packets between driver and usb
device.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>