vcomp/cmpto_j2k: fixed misleading comments

Actually the pool properties is precompress_desc, saved_desc is used
in usual sense to check whether the properties were changed from last
(re)configuratio.

src/video_compress/cmpto_j2k.cpp

@@ -141,8 +141,8 @@ struct state_video_compress_j2k {
         unsigned int in_frames{};   ///< number of currently encoding frames
         mutex lock;
         condition_variable frame_popped;
-        video_desc saved_desc{}; ///< for pool reconfiguration
-        video_desc precompress_desc{};
+        video_desc saved_desc{};
+        video_desc precompress_desc{}; ///< pool properties
         video_desc compressed_desc{};
         void (*convertFunc)(video_frame *dst, video_frame *src){nullptr};
 };