[DAGCombine] Use isLegalExtLoad for MatchLoadCombine (#140536)

This looks wrong to me, but I don't have a test case where it alters the
generated code.

Author: davemgreen

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -9482,8 +9482,8 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
   // split into legal sized loads. This enables us to combine i64 load by i8
   // patterns to a couple of i32 loads on 32 bit targets.
   if (LegalOperations &&
-      !TLI.isOperationLegal(NeedsZext ? ISD::ZEXTLOAD : ISD::NON_EXTLOAD,
-                            MemVT))
+      !TLI.isLoadExtLegal(NeedsZext ? ISD::ZEXTLOAD : ISD::NON_EXTLOAD, VT,
+                          MemVT))
     return SDValue();
 
   // Check if the bytes of the OR we are looking at match with either big or