graphics/hvif-tools: fix build on ARM / POWER

/wrkdirs/usr/ports/graphics/hvif-tools/work/hvif-tools-2.1.0/src/tracer/processing/PathScanner.cpp:20:4: error: constant expression evaluates to -1 which cannot be narrowed to type 'char' [-Wc++11-narrowing]

20 |         {{-1,-1,-1,-1}, {-1,-1,-1,-1}, {-1,-1,-1,-1}, {-1,-1,-1,-1}}, // 0
   |           ^~

/wrkdirs/usr/ports/graphics/hvif-tools/work/hvif-tools-2.1.0/src/tracer/processing/PathScanner.cpp:20:4: note: insert an explicit cast to silence this issue

20 |         {{-1,-1,-1,-1}, {-1,-1,-1,-1}, {-1,-1,-1,-1}, {-1,-1,-1,-1}}, // 0
   |           ^~
   |           static_cast<char>( )