[mlir][NFC] Fix format specifier warning on Windows

`%ld` specifier is defined to work on values of type `long`. The parameter given to `fprintf` is of type `intptr_t` whose actual underlying integer type is unspecified. On Unix systems it happens to commonly be `long` but on 64-bit Windows it is defined as `long long`.

The cross-platform way to print a `intptr_t` is to use `PRIdPTR` which expands to the correct format specifier for `intptr_t`. This avoids any undefined behaviour and compiler warnings.