USB: host: ohci-at91: fix non static symbol warning

Fixes the following sparse warning:

drivers/usb/host/ohci-at91.c:141:15: warning:
 symbol 'at91_dt_syscon_sfr' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ohci-at91.c

@@ -138,7 +138,7 @@ static void at91_stop_hc(struct platform_device *pdev)
 
 static void usb_hcd_at91_remove (struct usb_hcd *, struct platform_device *);
 
-struct regmap *at91_dt_syscon_sfr(void)
+static struct regmap *at91_dt_syscon_sfr(void)
 {
 	struct regmap *regmap;