S/390: Add fallthrough comment in md file.

gcc/ChangeLog:

2016-10-20  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* config/s390/s390.md ("prefetch"): Add fallthrough comment.

From-SVN: r241362

gcc/ChangeLog

+2016-10-20  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
+
+	* config/s390/s390.md ("prefetch"): Add fallthrough comment.
+
 2016-10-20  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
 
 	PR tree-optimization/53979

gcc/config/s390/s390.md

@@ -10629,6 +10629,7 @@
       case 1:
         if (larl_operand (operands[0], Pmode))
 	  return INTVAL (operands[1]) == 1 ? "pfdrl\t2,%a0" : "pfdrl\t1,%a0";
+	  /* fallthrough */
       default:
 
         /* This might be reached for symbolic operands with an odd