ath6kl: fix regression in ath6kl_upload_board_file()

My patch 24fc32b3 ("ath6kl: add ath6kl_bmi_write_hi32()") caused a regression
in ath6kl_upload_board_file() and the board_address variable was not
properly initialised in some cases:

ath6kl/init.c:1068:6: warning: ‘board_address’ may be used uninitialized
in this function

Most likely this broke ar6004 support but I can't test that right now.
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath6kl/init.c

@@ -1078,8 +1078,9 @@ static int ath6kl_upload_board_file(struct ath6kl *ar)
 	 * writing board data.
 	 */
 	if (ar->hw.board_addr != 0) {
+		board_address = ar->hw.board_addr;
 		ath6kl_bmi_write_hi32(ar, hi_board_data,
-				      ar->hw.board_addr);
+				      board_address);
 	} else {
 		ath6kl_bmi_read_hi32(ar, hi_board_data, &board_address);
 	}