staging: brcm80211: removed unneeded call to brcms_b_tx_fifo_suspended

- removed call to brcms_b_tx_fifo_suspended on receipt of TX FIFO suspend/flush
  completion signal.
- removed brcms_b_tx_fifo_suspended function as it is not being used elsewhere.

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