spi/rockchip: fix error return code in rockchip_spi_probe()

Fix to return -EINVAL from the error handling case instead of 0 when
failed to get fifo length.

Signed-off-by: Wei Yongjun <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-rockchip.c

···
 	rs->fifo_len = get_fifo_len(rs);
 	if (!rs->fifo_len) {
 		dev_err(&pdev->dev, "Failed to get fifo length\n");
+		ret = -EINVAL;
 		goto err_get_fifo_len;
 	}