spi: fsl-spi: Do not check 0 for platform_get_irq()

Since platform_get_irq() never returned zero, so it need not to check
whether it returned zero, and we use the return error code of
platform_get_irq() to replace the current return error code, for that
platform_get_irq() may return -EINVAL or -ENXIO.

Signed-off-by: Zhu Wang <wangzhu9@huawei.com>
Link: https://lore.kernel.org/r/20230803083944.21501-1-wangzhu9@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>