staging: brcm80211: convert endianess before handling the frame

The received frame from the device is in little-endian order and
converted in the receive path. However, the phy code was doing
the rssi calculation with packet in LE order. This has been changed
to do the le_to_cpu conversion before doing the rssi computation
and further receive processing.

Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>