Fix blocking when tag is on the reader for some time

Taken from pi-rc522 PR#49:
ondryaso#49

Author: fladi

pyrc522/rfid.py

@@ -400,6 +400,9 @@ def wait_for_tag(self):
         # wait for it
         waiting = True
         while waiting:
+            self.init()
+            self.dev_write(0x04, 0x00)
+            self.dev_write(0x02, 0xA0)
             self.dev_write(0x09, 0x26)
             self.dev_write(0x01, 0x0C)
             self.dev_write(0x0D, 0x87)