apdu_split.py: Changed buf data type list to array

The data type of incoming and outgoing data should be the same
at all points of the program to make it consistent.
For this program the data type is array.array.

usb_application/apdu_split.py

@@ -35,9 +35,9 @@ class Apdu_splitter:
 
     def __init__(self):
         self.state = apdu_states.APDU_S_CLA
-        self.buf = []
-        self.pts_buf = []
-        self.data = []
+        self.buf = array('B', [])
+        self.pts_buf = array('B', [])
+        self.data = array('B', [])
         self.ins = array('B', [])
         self.data_remainig = 0