avdevice: Give names to anonymously typedeffed structs

Anonymous structs can cause trouble in header files, so try to
avoid them altogether as a matter of good style.

libavdevice/bktr.c

@@ -51,7 +51,7 @@
 #include <signal.h>
 #include <stdint.h>
 
-typedef struct {
+typedef struct VideoData {
     AVClass *class;
     int video_fd;
     int tuner_fd;

libavdevice/fbdev.c

@@ -76,7 +76,7 @@ static enum AVPixelFormat get_pixfmt_from_fb_varinfo(struct fb_var_screeninfo *v
     return AV_PIX_FMT_NONE;
 }
 
-typedef struct {
+typedef struct FBDevContext {
     AVClass *class;          ///< class for private options
     int frame_size;          ///< size in bytes of a grabbed frame
     AVRational framerate_q;  ///< framerate

libavdevice/jack_audio.c

@@ -38,7 +38,7 @@
  */
 #define FIFO_PACKETS_NUM 16
 
-typedef struct {
+typedef struct JackData {
     AVClass        *class;
     jack_client_t * client;
     int             activated;

libavdevice/oss_audio.c

@@ -44,7 +44,7 @@
 
 #define AUDIO_BLOCK_SIZE 4096
 
-typedef struct {
+typedef struct AudioData {
     AVClass *class;
     int fd;
     int sample_rate;