targets/acorn_cle_215: fix typo in description.

litex_boards/targets/acorn_cle_215.py

@@ -197,7 +197,7 @@ class PCIeSoC(SoCCore):
 # Build --------------------------------------------------------------------------------------------
 
 def main():
-    parser = argparse.ArgumentParser(description="LiteX SoC on LiteX SoC on Acorn CLE 215+")
+    parser = argparse.ArgumentParser(description="LiteX SoC on Acorn CLE 215+")
     parser.add_argument("--build", action="store_true", help="Build bitstream")
     parser.add_argument("--load",  action="store_true", help="Load bitstream")
     parser.add_argument("--flash", action="store_true", help="Flash bitstream")