staging/btmtk_usb: Mark local functions as static

sparse complains about some local functions not being static:
drivers/staging/btmtk_usb/btmtk_usb.c:50:6:
warning: symbol 'hex_dump' was not declared. Should it be static?
drivers/staging/btmtk_usb/btmtk_usb.c:227:5:
warning: symbol 'checksume16' was not declared. Should it be static?

-> add the static keyword
Signed-off-by: NPeter Huewe <peterhuewe@gmx.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/btmtk_usb/btmtk_usb.c

@@ -47,7 +47,7 @@ static struct usb_driver btmtk_usb_driver;
 static int btmtk_usb_load_rom_patch(struct btmtk_usb_data *);
 static int btmtk_usb_load_fw(struct btmtk_usb_data *);
 
-void hex_dump(char *str, u8 *src_buf, u32 src_buf_len)
+static void hex_dump(char *str, u8 *src_buf, u32 src_buf_len)
 {
 	unsigned char *pt;
 	int x;
@@ -224,7 +224,7 @@ static void btmtk_usb_cap_init(struct btmtk_usb_data *data)
 	}
 }
 
-u16 checksume16(u8 *pData, int len)
+static u16 checksume16(u8 *pData, int len)
 {
 	int sum = 0;