spi: dw: Fix error return code in dw_spi_bt1_probe()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: abf00907

 ("spi: dw: Add Baikal-T1 SPI Controller glue driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/1607071357-33378-1-git-send-email-zhangchangzhong@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>