tests: lib: gui: lvgl: Add fs_file_t type variable initializations

The commit adds initializations of fs_file_t variables in preparation
for fs_open function change that will require fs_file_t object, passed
to the function, to be initialized before first usage.

Signed-off-by: Dominik Ermel <[email protected]>

Author: de-nordic

tests/lib/gui/lvgl/src/main.c

@@ -91,6 +91,7 @@ void setup_fs(void)
 		return;
 	}
 
+	fs_file_t_init(&img);
 	ret = fs_open(&img, IMG_FILE_PATH, FS_O_CREATE | FS_O_WRITE);
 	if (ret < 0) {
 		TC_PRINT("Failed to open image file: %d\n", ret);