gdb/copyright.py: Adjust following rename of sim/ppc/ppc-instructions...

... to sim/ppc/powerpc.igen

This file is in the NOT_FSF_LIST because this file has a copyright
which is not assigned to the FSF. Since the file got renamed,
the corresponding entry in NOT_FSF_LIST needs to be renamed as well.
diff --git a/gdb/copyright.py b/gdb/copyright.py
index 040fed1..c69d76b 100755
--- a/gdb/copyright.py
+++ b/gdb/copyright.py
@@ -365,7 +365,7 @@
     "sim/ppc/hw_trace.c",
     "sim/ppc/emul_netbsd.h",
     "sim/ppc/psim.c",
-    "sim/ppc/ppc-instructions",
+    "sim/ppc/powerpc.igen",
     "sim/ppc/tree.h",
     "sim/ppc/README",
     "sim/ppc/gen-icache.h",