S390: Change LoadP to LoadB for TestIfSmi

R=jyan@ca.ibm.com, joransiu@ca.ibm.com,

BUG=

Review-Url: https://codereview.chromium.org/2588163002
Cr-Commit-Position: refs/heads/master@{#41829}

src/s390/macro-assembler-s390.h

@@ -1539,7 +1539,7 @@ class MacroAssembler : public Assembler {
     } else if (is_int20(value.offset())) {
       tmy(value, Operand(1));
     } else {
-      LoadP(r0, value);
+      LoadB(r0, value);
       tmll(r0, Operand(1));
     }
   }