[SH] Use more braced strings in MD

[Oleg Endo]

Hello,

Like the topic says.  No functional change, just cosmetics.
Tested on rev 191342 with 
make -k check RUNTESTFLAGS="--target_board=sh-sim
\{-m2/-ml,-m2/-mb,-m2a/-mb,-m4/-ml,-m4/-mb,-m4a/-ml,-m4a/-mb}"

and no new failures.
OK to install?

Cheers,
Oleg

ChangeLog:

        * config/sh/sh.md (prologue, epilogue): Use braced strings.

Index: gcc/config/sh/sh.md
===================================================================
--- gcc/config/sh/sh.md	(revision 191342)
+++ gcc/config/sh/sh.md	(working copy)
@@ -10303,12 +10303,17 @@
 (define_expand "prologue"
   [(const_int 0)]
   ""
-  "sh_expand_prologue (); DONE;")
+{
+  sh_expand_prologue ();
+  DONE;
+})
 
 (define_expand "epilogue"
   [(return)]
   ""
-  "sh_expand_epilogue (false);")
+{
+  sh_expand_epilogue (false);
+})
 
 (define_expand "eh_return"
   [(use (match_operand 0 "register_operand" ""))]