spi: Delete useless checks

Since "res" will never be null, just delete this check.

Signed-off-by: zhang jiao <zhangjiao2@cmss.chinamobile.com>
Link: https://patch.msgid.link/20241112081637.40962-1-zhangjiao2@cmss.chinamobile.com


Signed-off-by: Mark Brown <broonie@kernel.org>