remove unnecessary obstack_finish

[Alan Modra]

Since I've been looking over the gas obstack code, here's a small
improvement.

It isn't necessary to call obstack_finish before obstack_free of an
unwanted string.

	* config/tc-mips.c (mips_parse_arguments): Replace obstack_finsih
	with obstack_base.

diff --git a/gas/config/tc-mips.c b/gas/config/tc-mips.c
index 7d0d8559115..f3a9875dcd1 100644
--- a/gas/config/tc-mips.c
+++ b/gas/config/tc-mips.c
@@ -3377,7 +3377,7 @@ mips_parse_arguments (char *s, char float_format)
       if (!s)
 	{
 	  obstack_free (&mips_operand_tokens,
-			obstack_finish (&mips_operand_tokens));
+			obstack_base (&mips_operand_tokens));
 	  return 0;
 	}
       SKIP_SPACE_TABS (s);

-- 
Alan Modra