Add the missing iounmap() before return from of_fsl_spi_probe()
in the error handling case.

Fixes: 0f0581b2 ("spi: fsl: Convert to use CS GPIO descriptors")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20210401140350.1677925-1-yangyingliang@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>