libplacebo: display: fix variable type
pl-output-hint is an integer variable, and it was leading to warnings when compiling:
../../modules/video_output/libplacebo/display.c: In function 'UpdateColorspaceHint':
../../modules/video_output/libplacebo/display.c:499:5: warning: case label value exceeds maximum value for type [-Wswitch-outside-range]
499 | case OUTPUT_HDR10:
| ^~~~
../../modules/video_output/libplacebo/display.c:503:5: warning: case label value exceeds maximum value for type [-Wswitch-outside-range]
503 | case OUTPUT_HLG:
| ^~~~
../../modules/video_output/libplacebo/display.c:477:5: warning: switch condition has boolean value [-Wswitch-bool]
477 | switch (var_InheritBool(vd, "pl-output-hint")) {
| ^~~~~~