samples: drivers: video: set an initial video buffer

Provide an initial video buffer in the first call to video_dequeue().
It is used by the driver for choosing between the input or output queue.
Applied to capture, capture_to_lvgl and tcpserversink samples.

Signed-off-by: Josuah Demangeon <me@josuah.net>

Author: josuah

samples/drivers/video/capture/src/main.c

@@ -90,7 +90,8 @@ static inline void video_display_frame(const struct device *const display_dev,
 
 int main(void)
 {
-	struct video_buffer *buffers[CONFIG_VIDEO_BUFFER_POOL_NUM_MAX], *vbuf;
+	struct video_buffer *buffers[CONFIG_VIDEO_BUFFER_POOL_NUM_MAX];
+	struct video_buffer *vbuf = &(struct video_buffer){};
 	struct video_format fmt;
 	struct video_caps caps;
 	struct video_frmival frmival;

samples/drivers/video/capture_to_lvgl/src/main.c

@@ -19,7 +19,8 @@ LOG_MODULE_REGISTER(main);
 
 int main(void)
 {
-	struct video_buffer *buffers[2], *vbuf;
+	struct video_buffer *buffers[2];
+	struct video_buffer *vbuf = &(struct video_buffer){};
 	const struct device *display_dev;
 	struct video_format fmt;
 	struct video_caps caps;

samples/drivers/video/tcpserversink/src/main.c

@@ -38,7 +38,8 @@ int main(void)
 {
 	struct sockaddr_in addr, client_addr;
 	socklen_t client_addr_len = sizeof(client_addr);
-	struct video_buffer *buffers[2], *vbuf;
+	struct video_buffer *buffers[2];
+	struct video_buffer *vbuf = &(struct video_buffer){};
 	int i, ret, sock, client;
 	struct video_format fmt;
 	struct video_caps caps;