brcmfmac: add kerneldoc for struct brcmf_bus::msgbuf

This field did not have kerneldoc description so adding it now.
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/broadcom/brcm80211/brcmfmac/bus.h

@@ -140,6 +140,7 @@ struct brcmf_bus_stats {
  * @always_use_fws_queue: bus wants use queue also when fwsignal is inactive.
  * @wowl_supported: is wowl supported by bus driver.
  * @chiprev: revision of the dongle chip.
+ * @msgbuf: msgbuf protocol parameters provided by bus layer.
  */
 struct brcmf_bus {
 	union {