drm/i915/scaler: Make scaler in_use a bool

Make scaler in_use a boolean since that's how it's used.

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241107122658.21901-8-ville.syrjala@linux.intel.com