[AMDGPU] Remove an unnecessary cast (NFC) (llvm#151279)

value() already returns uint64_t.

Author: kazutakahirata

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -4292,7 +4292,7 @@ SDValue SITargetLowering::LowerDYNAMIC_STACKALLOC(SDValue Op,
   Chain = BaseAddr.getValue(1);
   Align StackAlign = TFL->getStackAlign();
   if (Alignment > StackAlign) {
-    uint64_t ScaledAlignment = (uint64_t)Alignment.value()
+    uint64_t ScaledAlignment = Alignment.value()
                                << Subtarget->getWavefrontSizeLog2();
     uint64_t StackAlignMask = ScaledAlignment - 1;
     SDValue TmpAddr = DAG.getNode(ISD::ADD, dl, VT, BaseAddr,