s390: preserve src register in MovIntToFloat

The conversion instr was being called twice and
the src register was not restored after the shift.

R=joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2527873003
Cr-Commit-Position: refs/heads/master@{#41269}

src/s390/macro-assembler-s390.cc

@@ -3831,8 +3831,8 @@ void MacroAssembler::SubP(Register dst, const MemOperand& opnd) {
 }
 
 void MacroAssembler::MovIntToFloat(DoubleRegister dst, Register src) {
-  sllg(src, src, Operand(32));
-  ldgr(dst, src);
+  sllg(r0, src, Operand(32));
+  ldgr(dst, r0);
 }
 
 void MacroAssembler::MovFloatToInt(Register dst, DoubleRegister src) {