Staging: wlan-ng: Fix Sparse warning should it be static?

This patch fixes following Sparse warning should it be static? in
staging/wlan-ng.
Signed-off-by: Tugce Sirin <ztugcesirin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wlan-ng/prism2fw.c

@@ -201,7 +201,7 @@ static int validate_identity(void);
 *	0	- success
 *	~0	- failure
 ----------------------------------------------------------------*/
-int prism2_fwtry(struct usb_device *udev, wlandevice_t *wlandev)
+static int prism2_fwtry(struct usb_device *udev, wlandevice_t *wlandev)
 {
 	const struct firmware *fw_entry = NULL;