pylibfdt: check_err accepts only integer as a first argument.

A list passed as an argument to check_err() means that
there is no error code to check and therefore it should
be returned back.

Signed-off-by: Lumir Balhar <lbalhar@redhat.com>
Message-Id: <20190218164856.23861-2-frenzy@frenzy.cz>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

pylibfdt/libfdt.i

@@ -137,7 +137,7 @@ def check_err(val, quiet=()):
     Raises
         FdtException if val < 0
     """
-    if val < 0:
+    if isinstance(val, int) and val < 0:
         if -val not in quiet:
             raise FdtException(val)
     return val