brcmfmac: prevent possible race condition on usb rx control.

brcmf_usb_tx_ctlpkt sends message using brcmf_usb_send_ctl then
clears boolean and waits for boolean to be set (by another
thread). This can result in situation where flag gets cleared
while result was already received. First clearing the flag and
then sending the data will prevent this.

Reviewed-by: Arend Van Spriel (arend@broadcom.com)
Reviewed-by: Franky (Zhenhui) Lin <frankyl@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>