rsi: Add descriptions for rsi_set_vap_capabilities()'s parameters

Fixes the following W=1 kernel build warning(s):

 drivers/net/wireless/rsi/rsi_91x_mgmt.c:713: warning: Function parameter or member 'mac_addr' not described in 'rsi_set_vap_capabilities'
 drivers/net/wireless/rsi/rsi_91x_mgmt.c:713: warning: Function parameter or member 'vap_id' not described in 'rsi_set_vap_capabilities'
 drivers/net/wireless/rsi/rsi_91x_mgmt.c:713: warning: Function parameter or member 'vap_status' not described in 'rsi_set_vap_capabilities'

Cc: Amitkumar Karwar <amitkarwar@gmail.com>
Cc: Siva Rebbagondla <siva8118@gmail.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200821071644.109970-7-lee.jones@linaro.org

drivers/net/wireless/rsi/rsi_91x_mgmt.c

@@ -702,6 +702,9 @@ static int rsi_program_bb_rf(struct rsi_common *common)
  * rsi_set_vap_capabilities() - This function send vap capability to firmware.
  * @common: Pointer to the driver private structure.
  * @mode: Operating mode of device.
+ * @mac_addr: MAC address
+ * @vap_id: Rate information - offset and mask
+ * @vap_status: VAP status - ADD, DELETE or UPDATE
  *
  * Return: 0 on success, corresponding negative error code on failure.
  */