wlcore: spi: fix non static symbol warning

Fixes the following sparse warning:

drivers/net/wireless/ti/wlcore/spi.c:87:34: warning:
 symbol 'wilink_data' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ti/wlcore/spi.c

@@ -84,7 +84,7 @@ struct wilink_familiy_data {
 	char name[8];
 };
 
-const struct wilink_familiy_data *wilink_data;
+static const struct wilink_familiy_data *wilink_data;
 
 static const struct wilink_familiy_data wl18xx_data = {
 	.name = "wl18xx",