Fix braino in BoundsCheckSlowPathX86_64.

No need to call AsArrayLength again.

Test: build
Change-Id: Id8dac5903646a2491d67f361ca8b384092a51e0f
diff --git a/compiler/optimizing/code_generator_x86_64.cc b/compiler/optimizing/code_generator_x86_64.cc
index b07949f..6de5e9c 100644
--- a/compiler/optimizing/code_generator_x86_64.cc
+++ b/compiler/optimizing/code_generator_x86_64.cc
@@ -196,7 +196,7 @@
     if (array_length->IsArrayLength() && array_length->IsEmittedAtUseSite()) {
       // Load the array length into our temporary.
       HArrayLength* length = array_length->AsArrayLength();
-      uint32_t len_offset = CodeGenerator::GetArrayLengthOffset(length->AsArrayLength());
+      uint32_t len_offset = CodeGenerator::GetArrayLengthOffset(length);
       Location array_loc = array_length->GetLocations()->InAt(0);
       Address array_len(array_loc.AsRegister<CpuRegister>(), len_offset);
       length_loc = Location::RegisterLocation(calling_convention.GetRegisterAt(1));