modules: lvgl: don't try to open file in read mode with create flag set

Current code would have systematically tried to add the FS_O_CREATE flag
when opening a file in read mode. This effectively made it impossible to
open files to read them on read-only file systems.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

modules/lvgl/lvgl_fs.c

@@ -56,17 +56,21 @@ static lv_fs_res_t errno_to_lv_fs_res(int err)
 static void *lvgl_fs_open(lv_fs_drv_t *drv, const char *path, lv_fs_mode_t mode)
 {
 	int err;
-	int zmode = FS_O_CREATE;
+	int zmode = 0;
 	void *file;
 
 	/* LVGL is passing absolute paths without the root slash add it back
 	 * by decrementing the path pointer.
 	 */
 	path--;
 
-	zmode |= (mode & LV_FS_MODE_WR) ? FS_O_WRITE : 0;
+	zmode |= (mode & LV_FS_MODE_WR) ? FS_O_WRITE | FS_O_CREATE : 0;
 	zmode |= (mode & LV_FS_MODE_RD) ? FS_O_READ : 0;
 
+	if (zmode == 0) {
+		return NULL;
+	}
+
 	file = lv_malloc(sizeof(struct fs_file_t));
 	if (!file) {
 		return NULL;