brcmfmac: no fws locking outside fws module.

FWS uses locking to protect its data while being called from
various entries. On bus_txdata the lock was kept resulting in
unnecessary long locking, but also creating possibility for
deadlock. This update changes the locking to release lock when
bus_txdata is called.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>