fix: specify enum modifier in sd_set_preview_callback signature (#959)

Author: newfla

stable-diffusion.h

@@ -267,7 +267,7 @@ typedef void (*sd_preview_cb_t)(int step, int frame_count, sd_image_t* frames, b
 
 SD_API void sd_set_log_callback(sd_log_cb_t sd_log_cb, void* data);
 SD_API void sd_set_progress_callback(sd_progress_cb_t cb, void* data);
-SD_API void sd_set_preview_callback(sd_preview_cb_t cb, preview_t mode, int interval, bool denoised, bool noisy);
+SD_API void sd_set_preview_callback(sd_preview_cb_t cb, enum preview_t mode, int interval, bool denoised, bool noisy);
 SD_API int32_t get_num_physical_cores();
 SD_API const char* sd_get_system_info();