tools: env: Avoid an uninited warning with was_locked

Set this variable to 0 to avoid a warning about an unused variable. This
happens on gcc 7.5.0 for me.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/env/fw_env.c

@@ -995,7 +995,7 @@ static int flash_write_buf(int dev, int fd, void *buf, size_t count)
 				   of the data */
 	loff_t blockstart;	/* running start of the current block -
 				   MEMGETBADBLOCK needs 64 bits */
-	int was_locked;		/* flash lock flag */
+	int was_locked = 0;	/* flash lock flag */
 	int rc;
 
 	/*