X64 Crankshaft: Fix unrestored context register in Math.power.

Review URL: http://codereview.chromium.org/6649020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7107 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-codegen-x64.cc

@@ -2563,6 +2563,8 @@ void LCodeGen::DoPower(LPower* instr) {
   }
   // Return value is in xmm0.
   __ movsd(result_reg, xmm0);
+  // Restore context register.
+  __ movq(rsi, Operand(rbp, StandardFrameConstants::kContextOffset));
 }