[primgen] Use SafeDumper for YAML

We did import this dumper, but didn't use it.

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/hw/ip/prim/util/primgen.py b/hw/ip/prim/util/primgen.py
index f8e3705..f601d50 100755
--- a/hw/ip/prim/util/primgen.py
+++ b/hw/ip/prim/util/primgen.py
@@ -378,7 +378,8 @@
                   f,
                   encoding="utf-8",
                   default_flow_style=False,
-                  sort_keys=False)
+                  sort_keys=False,
+                  Dumper=YamlDumper)
     print("Core file written to %s" % (abstract_prim_core_filepath, ))