brcmfmac: show firmware release info in ethtool driver info

The ethtool driver info already contained the unique firmware
identifier. This patch adds the firmware release version.

   $ ethtool -i wlan4
   driver: brcmfmac
   version: 6.10.224.22
   firmware-version: 01-32bd010f

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>