NFC: potential integer overflow problem in check_crc()

If "buf[0]" is 255 then "len" gets set to 0.  The call to
"crc_ccitt(0xffff, buf, len - 2);" casts the "len - 2" to a high
positive number which is ugly.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/nfc/pn544_hci.c

@@ -232,7 +232,7 @@ static int pn544_hci_i2c_write(struct i2c_client *client, u8 *buf, int len)
 
 static int check_crc(u8 *buf, int buflen)
 {
-	u8 len;
+	int len;
 	u16 crc;
 
 	len = buf[0] + 1;