brcmfmac: pass DEAUTH/DISASSOC reason code to user-space

The driver always called cfg80211_disconnected() with reason parameter
set to zero, ie. unknown. However, firmware does provide a valid
802.11 reason code in DEAUTH and DISASSOC event message to the driver.
This patch passes the reason code to cfg80211_disconnected().

Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
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: Kalle Valo <kvalo@codeaurora.org>