vd_lavc: increase the possible length of the hwdec name

this lead to an unexpected videotoolbox-copy hwdec name due to the last
two chars being cut off. since selection is also done by that name one
had to use "videotoolbox-co" to explicitly use the copy mode of
videotoolbox.

video/decode/vd_lavc.c

@@ -132,7 +132,7 @@ const struct m_sub_options vd_lavc_conf = {
 
 struct hwdec_info {
     char name[64];
-    char method_name[16]; // non-unique name describing the hwdec method
+    char method_name[24]; // non-unique name describing the hwdec method
     const AVCodec *codec; // implemented by this codec
     enum AVHWDeviceType lavc_device; // if not NONE, get a hwdevice
     bool copying; // if true, outputs sw frames, or copy to sw ourselves