tpm: sandbox: Change the return code when device is already open

All the TPM drivers as well as out TCG TIS API for a TPM2.0 device
return -EBUSY if the device has already been opened.  Adjust
the sandbox TPM do return the same error code.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

drivers/tpm/tpm2_tis_sandbox.c

@@ -810,7 +810,7 @@ static int sandbox_tpm2_open(struct udevice *dev)
 	struct sandbox_tpm2 *tpm = dev_get_priv(dev);
 
 	if (tpm->init_done)
-		return -EIO;
+		return -EBUSY;
 
 	tpm->init_done = true;