brcmfmac: rename brcmf_fws_mac_desc_ready()

Replace the function by brcmf_fws_mac_desc_closed(). The new function
is used in the transmit path and in the dequeue worker.

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