avcodec/h2645_parse: simplify memset call

Removed (new_size - pkt->nals_allocated) because this value is always 1
during the call.
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/h2645_parse.c

@@ -461,8 +461,7 @@ int ff_h2645_packet_split(H2645Packet *pkt, const uint8_t *buf, int length,
                 return AVERROR(ENOMEM);
 
             pkt->nals = tmp;
-            memset(pkt->nals + pkt->nals_allocated, 0,
-                   (new_size - pkt->nals_allocated) * sizeof(*pkt->nals));
+            memset(pkt->nals + pkt->nals_allocated, 0, sizeof(*pkt->nals));
 
             nal = &pkt->nals[pkt->nb_nals];
             nal->skipped_bytes_pos_size = 1024; // initial buffer size