[Target][ARM] Add a usage for SrcSz to unbreak build-bots without assertions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355101 91177308-0d34-0410-b5e6-96231b3b80d8

Author: kadircet

lib/Target/ARM/ARMISelLowering.cpp

@@ -13701,6 +13701,7 @@ void ARMTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
     EVT VT = Op.getValueType();
     const unsigned DstSz = VT.getScalarSizeInBits();
     const unsigned SrcSz = VecVT.getVectorElementType().getSizeInBits();
+    (void)SrcSz;
     assert(SrcSz == Known.getBitWidth());
     assert(DstSz > SrcSz);
     if (Op.getOpcode() == ARMISD::VGETLANEs)