Fix stride type
Fix stride type

Prevents the following compiler warning:

../src/decode.c:1979:32: warning: implicit conversion loses integer precision: 'const ptrdiff_t' (aka 'const long') to 'int' [-Wshorten-64-to-32]
            const int stride = f->cur.stride[!!p];
                      ~~~~~~   ^~~~~~~~~~~~~~~~~~
1 warning generated.

videolan/dav1d