load_camera: initialize with calloc to avoid uninitialized reads

in particular: if a sensor can't be found, then camera->sensor_path is
unassigned. this would cause a segfault later, in libmegapixels_open.

config/pine64,pinephone.conf

@@ -37,7 +37,7 @@ Rear: {
                 {Type: "Link", From: "ov5640", FromPad: 0, To: "sun6i-csi", ToPad: 0},
                 {Type: "Mode", Entity: "ov5640"}
             );
-        }
+        },
         {
             Width: 1280;
             Height: 720;

src/parse.c

@@ -191,10 +191,7 @@ load_camera(libmegapixels_devconfig *config, config_t *cfg, const char *name)
 		return -1;
 	}
 	libmegapixels_camera *camera;
-	camera = malloc(sizeof(libmegapixels_camera));
-	camera->sensor_fd = 0;
-	camera->media_fd = 0;
-	camera->video_fd = 0;
+	camera = calloc(1, sizeof(libmegapixels_camera));
 
 	int res = find_media_node(camera, bridge_driver, sensor_driver);
 	if (res < 0) {