MIPS: Fix '[regexp] implement case-insensitive unicode regexps.'

TEST=mjsunit/harmony/unicode-regexp-ignore-case
BUG=

Review URL: https://codereview.chromium.org/1639263002

Cr-Commit-Position: refs/heads/master@{#33553}

src/regexp/mips/regexp-macro-assembler-mips.cc

@@ -326,7 +326,7 @@ void RegExpMacroAssemblerMIPS::CheckNotBackReferenceIgnoreCase(
     // Isolate.
 #ifdef V8_I18N_SUPPORT
     if (unicode) {
-      __ li(a3, Operand(zero_reg));
+      __ mov(a3, zero_reg);
     } else  // NOLINT
 #endif      // V8_I18N_SUPPORT
     {

src/regexp/mips64/regexp-macro-assembler-mips64.cc

@@ -362,7 +362,7 @@ void RegExpMacroAssemblerMIPS::CheckNotBackReferenceIgnoreCase(
     // Isolate.
 #ifdef V8_I18N_SUPPORT
     if (unicode) {
-      __ li(a3, Operand(zero_reg));
+      __ mov(a3, zero_reg);
     } else  // NOLINT
 #endif      // V8_I18N_SUPPORT
     {