v4l2enc: adding AVClass

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit fcb11ec2)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/v4l2enc.c

@@ -22,6 +22,7 @@
 #include "avdevice.h"
 
 typedef struct {
+    AVClass *class;
     int fd;
 } V4L2Context;