staging: brcm80211: changing interface to n-phy rssi compute function

The function wlc_phy_rssi_compute_nphy() was called with pointer to
brcms_d11rxhdr structure in which it filled in the received power
per antenna. However, these are not used further in the driver so
it only needs the d11rxhdr structure as input for rssi calculation.

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>