another minor Xtensa cleanup

[Bob Wilson <bwilson at tensilica dot com>]

There is an initialization function for Xtensa "tinsn" structures in GAS, but in 
some places, memset was being used to clear them instead.  If we're going to 
have such a function, we might as well use it.  Tested with an xtensa-elf build 
and committed.

gas/
	* config/tc-xtensa.c (xg_build_to_insn): Use tinsn_init.
	(xg_expand_assembly_insn, istack_push_space, istack_pop): Likewise.

Index: config/tc-xtensa.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-xtensa.c,v
retrieving revision 1.76
diff -u -p -r1.76 tc-xtensa.c
--- config/tc-xtensa.c	2 Feb 2007 23:59:29 -0000	1.76
+++ config/tc-xtensa.c	3 Feb 2007 00:06:18 -0000
@@ -3309,7 +3309,7 @@ xg_build_to_insn (TInsn *targ, TInsn *in
   BuildOp *op;
   symbolS *sym;
 
-  memset (targ, 0, sizeof (TInsn));
+  tinsn_init (targ);
   targ->linenum = insn->linenum;
   switch (bi->typ)
     {
@@ -3858,7 +3858,7 @@ xg_expand_assembly_insn (IStack *istack,
   TInsn new_insn;
   bfd_boolean do_expand;
 
-  memset (&new_insn, 0, sizeof (TInsn));
+  tinsn_init (&new_insn);
 
   /* Narrow it if we can.  xg_simplify_insn now does all the
      appropriate checking (e.g., for the density option).  */
@@ -11009,7 +11009,7 @@ istack_push_space (IStack *stack)
   TInsn *insn;
   assert (!istack_full (stack));
   insn = &stack->insn[rec];
-  memset (insn, 0, sizeof (TInsn));
+  tinsn_init (insn);
   stack->ninsn++;
   return insn;
 }
@@ -11024,7 +11024,7 @@ istack_pop (IStack *stack)
   int rec = stack->ninsn - 1;
   assert (!istack_empty (stack));
   stack->ninsn--;
-  memset (&stack->insn[rec], 0, sizeof (TInsn));
+  tinsn_init (&stack->insn[rec]);
 }