[mlir] Fix -Wdeprecated-declarations of cast in VCIXToLLVMIRTranslation.cpp (NFC)

In file included from /llvm-project/mlir/lib/Target/LLVMIR/Dialect/VCIX/VCIXToLLVMIRTranslation.cpp:70:
/llvm-project/build-Release/tools/mlir/include/mlir/Dialect/LLVMIR/VCIXConversions.inc:8:48: error: 'cast' is deprecated: Use mlir::cast<U>() instead [-Werror,-Wdeprecated-declarations]
      VectorType vt = op.getResult().getType().cast<VectorType>();
                                               ^
/llvm-project/mlir/include/mlir/IR/Types.h:345:9: note: 'cast' has been explicitly marked deprecated here
U Type::cast() const {
        ^
In file included from /llvm-project/mlir/lib/Target/LLVMIR/Dialect/VCIX/VCIXToLLVMIRTranslation.cpp:70:
/llvm-project/build-Release/tools/mlir/include/mlir/Dialect/LLVMIR/VCIXConversions.inc:8:48: error: 'cast<mlir::VectorType>' is deprecated: Use mlir::cast<U>() instead [-Werror,-Wdeprecated-declarations]
      VectorType vt = op.getResult().getType().cast<VectorType>();
                                               ^
/llvm-project/mlir/include/mlir/IR/Types.h:112:5: note: 'cast<mlir::VectorType>' has been explicitly marked deprecated here
  [[deprecated("Use mlir::cast<U>() instead")]]
    ^
In file included from /llvm-project/mlir/lib/Target/LLVMIR/Dialect/VCIX/VCIXToLLVMIRTranslation.cpp:70:
/llvm-project/build-Release/tools/mlir/include/mlir/Dialect/LLVMIR/VCIXConversions.inc:32:48: error: 'cast' is deprecated: Use mlir::cast<U>() instead [-Werror,-Wdeprecated-declarations]
      VectorType vt = op.getResult().getType().cast<VectorType>();
                                               ^
/llvm-project/mlir/include/mlir/IR/Types.h:345:9: note: 'cast' has been explicitly marked deprecated here
U Type::cast() const {
        ^
In file included from /llvm-project/mlir/lib/Target/LLVMIR/Dialect/VCIX/VCIXToLLVMIRTranslation.cpp:70:
/llvm-project/build-Release/tools/mlir/include/mlir/Dialect/LLVMIR/VCIXConversions.inc:32:48: error: 'cast<mlir::VectorType>' is deprecated: Use mlir::cast<U>() instead [-Werror,-Wdeprecated-declarations]
      VectorType vt = op.getResult().getType().cast<VectorType>();
                                               ^
/llvm-project/mlir/include/mlir/IR/Types.h:112:5: note: 'cast<mlir::VectorType>' has been explicitly marked deprecated here
  [[deprecated("Use mlir::cast<U>() instead")]]
    ^
4 errors generated.