executorch/examples/portable/custom_ops/custom_ops_2_out.cpp: fix llvm-17-exposed format mismatches

Summary:
This avoids the following errors:

  executorch/examples/portable/custom_ops/custom_ops_2_out.cpp:23:7: error: format specifies type 'char' but the argument has type 'ScalarType' [-Werror,-Wformat]
  executorch/examples/portable/custom_ops/custom_ops_2_out.cpp:27:7: error: format specifies type 'char' but the argument has type 'ScalarType' [-Werror,-Wformat]

Differential Revision: D64656845

Author: Jim Meyering

examples/portable/custom_ops/custom_ops_2_out.cpp

@@ -20,11 +20,11 @@ void check_preconditions(const Tensor& in, Tensor& out) {
   ET_CHECK_MSG(
       out.scalar_type() == ScalarType::Float,
       "Expected out tensor to have dtype Float, but got %hhd instead",
-      out.scalar_type());
+      static_cast<int8_t>(out.scalar_type()));
   ET_CHECK_MSG(
       in.scalar_type() == ScalarType::Float,
       "Expected in tensor to have dtype Float, but got %hhd instead",
-      in.scalar_type());
+      static_cast<int8_t>(in.scalar_type()));
   ET_CHECK_MSG(
       out.dim() == in.dim(),
       "Number of dims of out tensor is not compatible with inputs");