Changed path to lib in mux_gen.py to a relative path

Signed-off-by: Grzegorz Latosinski <glatosinski@antmicro.com>

v2x/mux_gen.py

diff --git a/v2x/mux_gen.py b/v2x/mux_gen.py
index 307ab93..e3953c3 100755
--- a/v2x/mux_gen.py
+++ b/v2x/mux_gen.py
@@ -13,9 +13,9 @@
 import os
 import sys
 
-from lib import mux as mux_lib
-from lib.argparse_extra import ActionStoreBool
-from lib.asserts import assert_eq
+from .lib import mux as mux_lib
+from .lib.argparse_extra import ActionStoreBool
+from .lib.asserts import assert_eq
 
 parser = argparse.ArgumentParser(
     description='Generate a MUX wrapper.',