Fixed signedness comparison warning

[radarhere]

https://github.com/python-pillow/Pillow/actions/runs/5186598166/jobs/9347921664#step:7:118

src/libImaging/Jpeg2KEncode.c: In function ‘j2k_encode_entry’:
src/libImaging/Jpeg2KEncode.c:467:27: warning: comparison of integer expressions of different signedness: ‘unsigned int’ and ‘int’ [-Wsign-compare]
467 | while (tile_width < (1 << (params.numresolution - 1U)) || tile_height < (1 << (params.numresolution - 1U))) {
| ^
src/libImaging/Jpeg2KEncode.c:467:79: warning: comparison of integer expressions of different signedness: ‘unsigned int’ and ‘int’ [-Wsign-compare]
467 | while (tile_width < (1 << (params.numresolution - 1U)) || tile_height < (1 << (params.numresolution - 1U))) {
| ^