[RS6000] Fix wrong mode reg

Fix thinko in rev 239011 (git d1d05ab7).

	* config/rs6000/rs6000.md (fix_trunc<mode>si2): Fix mode of reg.

From-SVN: r239217

gcc/ChangeLog

+2016-08-07  Alan Modra  <amodra@gmail.com>
+
+	* config/rs6000/rs6000.md (fix_trunc<mode>si2): Fix mode of reg.
+
 2016-08-07  Kugan Vivekanandarajah  <kuganv@linaro.org>
 
 	* data-streamer-in.c (streamer_read_wide_int): New.

gcc/config/rs6000/rs6000.md

@@ -5357,7 +5357,7 @@
 {
   if (!<E500_CONVERT>)
     {
-      rtx src = force_reg (SFmode, operands[1]);
+      rtx src = force_reg (<MODE>mode, operands[1]);
 
       if (TARGET_STFIWX)
 	emit_insn (gen_fix_trunc<mode>si2_stfiwx (operands[0], src));