staging: brcm80211: rename external function in wl_cfg80211.c

Renamed external function getting rid of wl_ prefix. Removed unused
function from the API header file wl_cfg80211.h as it was not defined.

Signed-off-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>