spi: topcliff-pch: fix error return code in pch_spi_probe()

Fix to return -ENOMEM in the platform_device_alloc() error handling
case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>