Correct addition to frame length when reading

Author: dunkmann00

adafruit_pn532/adafruit_pn532.py

@@ -249,7 +249,7 @@ def _read_frame(self, length):
         might be returned!
         """
         # Read frame with expected length of data.
-        response = self._read_data(length + 8)
+        response = self._read_data(length + 7)
         if self.debug:
             print("Read frame:", [hex(i) for i in response])