pylibfdt: Return string instead of bytearray from getprop()

The return value is not actually mutable, so it seems more correct to
return bytes rather than a bytearray.

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

pylibfdt/libfdt.i

@@ -365,7 +365,7 @@ class Fdt:
             quiet: Errors to ignore (empty to raise on all errors)
 
         Returns:
-            Value of property as a bytearray, or -ve error number
+            Value of property as a string of bytes, or -ve error number
 
         Raises:
             FdtError if any error occurs (e.g. the property is not found)
@@ -374,7 +374,8 @@ class Fdt:
                                quiet)
         if isinstance(pdata, (int)):
             return pdata
-        return bytearray(pdata[0])
+        # Use bytes() rather than string(). This works on both Python 2 and 3
+        return bytes(pdata[0])
 
     def get_phandle(self, nodeoffset):
         """Get the phandle of a node