[AMDGPU] Add intrinsics for tbuffer load and store - build error fix

Variable was unused in non-debug build (used in assert) causing compile time
warning and eventual build failure

llvm-svn: 306034
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 880c0dd..000eaaf 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -3551,8 +3551,7 @@
      Op.getOperand(13), // slc
     };
 
-    const ConstantSDNode *tfe = cast<ConstantSDNode>(Op.getOperand(14));
-    assert(tfe->getZExtValue() == 0 &&
+    assert((cast<ConstantSDNode>(Op.getOperand(14)))->getZExtValue() == 0 &&
            "Value of tfe other than zero is unsupported");
 
     EVT VT = Op.getOperand(3).getValueType();