test/test_targets: use uart-name=stub.

test/test_targets.py

@@ -121,7 +121,7 @@ litex/boards/targets/simple.py litex.boards.platforms.{p} \
     --cpu-type=vexriscv     \
     --no-compile-software   \
     --no-compile-gateware   \
-    --uart-stub=True        \
+    --uart-name=stub        \
 """.format(p=p)
                 subprocess.check_call(cmd, shell=True)
 
@@ -142,7 +142,7 @@ litex/boards/targets/simple.py litex.boards.platforms.arty \
     --cpu-variant={v}       \
     --no-compile-software   \
     --no-compile-gateware   \
-    --uart-stub=True        \
+    --uart-name=stub        \
 """.format(c=cpu, v=variant)
         subprocess.check_output(cmd, shell=True)