Fix unused parameter warning

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/library/ecp.c b/library/ecp.c
index 0b2b59e..a7486c1 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -3040,6 +3040,8 @@
             goto cleanup;
         }
     }
+#else
+    (void) grp_id;
 #endif
 
     /* Final check: check if XmP + 1 is P (final because it changes XmP!) */