scripts: west: commands: build: fix pylint issue

Do not end except block with a useless return, use a pass instead. This
fixes pylint R1711: "Useless return at end of function or method
(useless-return)".

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
diff --git a/scripts/west_commands/build.py b/scripts/west_commands/build.py
index 56c463d..c137d1a 100644
--- a/scripts/west_commands/build.py
+++ b/scripts/west_commands/build.py
@@ -276,7 +276,7 @@
             if remainder:
                 self.args.cmake_opts = remainder
         except IndexError:
-            return
+            pass
 
     def _parse_test_item(self, test_item):
         found_test_metadata = False