staging: brcm80211: removed unused softmac transmit power variables

Struct member variables were only set to '0'. As a result, function
brcms_c_local_constraint_qdbm() always returned BRCMS_TXPWR_MAX and
thus could be removed.

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