[MLIR] Apply clang-tidy fixes for llvm-else-after-return in SPIRVCanonicalization.cpp (NFC)

Author: joker-eph

mlir/lib/Dialect/SPIRV/IR/SPIRVCanonicalization.cpp

@@ -251,9 +251,8 @@ struct MulExtendedFold final : OpRewritePattern<MulOp> {
         {lhsAttr, rhsAttr}, [](const APInt &a, const APInt &b) {
           if (IsSigned) {
             return llvm::APIntOps::mulhs(a, b);
-          } else {
-            return llvm::APIntOps::mulhu(a, b);
           }
+          return llvm::APIntOps::mulhu(a, b);
         });
 
     if (!highBits)