Fix generation of the subtitling descriptor

The generation function for the subtitling descriptor erroneously uses the
modulo operation instead of a bitwise AND.

(cherry picked from commit bc7bb320854b0d4bd4f74a5851be0852681d629d)
Signed-off-by: Jean-Paul Saman <jpsaman@videolan.org>

src/descriptors/dr_59.c

@@ -128,12 +128,12 @@ dvbpsi_descriptor_t * dvbpsi_GenSubtitlingDr(
         p_descriptor->p_data[8 * i + 4] =
                 p_decoded->p_subtitle[i].i_composition_page_id >> 8;
         p_descriptor->p_data[8 * i + 5] =
-                p_decoded->p_subtitle[i].i_composition_page_id % 0xFF;
+                p_decoded->p_subtitle[i].i_composition_page_id & 0xFF;
 
         p_descriptor->p_data[8 * i + 6] =
                 p_decoded->p_subtitle[i].i_ancillary_page_id >> 8;
         p_descriptor->p_data[8 * i + 7] =
-                p_decoded->p_subtitle[i].i_ancillary_page_id % 0xFF;
+                p_decoded->p_subtitle[i].i_ancillary_page_id & 0xFF;
     }
 
     if (b_duplicate)