Tools: Fix exception message with duplicated PIDs

The message which gets thrown in the exception when the manifest
list is parsed and duplicated PIDs are detected must correctly
print the duplicated PID value.

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: I6539f821146d22b86b9cff0ee212a4df21a3c970
diff --git a/tools/tfm_parse_manifest_list.py b/tools/tfm_parse_manifest_list.py
index d37d9a8..f1b5367 100644
--- a/tools/tfm_parse_manifest_list.py
+++ b/tools/tfm_parse_manifest_list.py
@@ -303,7 +303,7 @@
 
             # Check if partition ID is duplicated
             if pid in pid_list:
-                raise Exception('PID No. {pid} has already been used!'.format(pid))
+                raise Exception('PID No. {} has already been used!'.format(pid))
             else:
                 pid_list.append(pid)