spi: bcm-qspi: Fix error return code in bcm_qspi_probe()

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

Fixes: fa236a7e

 ("spi: bcm-qspi: Add Broadcom MSPI driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>