spi: spi-mem: Fix passing zero to 'PTR_ERR' warning

Fix smatch warning:

drivers/spi/spi-mem.c:746 spi_mem_probe() warn: passing zero to 'PTR_ERR'

Fixes: 5d27a9c8 ("spi: spi-mem: Extend the SPI mem interface to set a custom memory name")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20201031033042.42892-1-yuehaibing@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-mem.c

@@ -743,7 +743,7 @@ static int spi_mem_probe(struct spi_device *spi)
 		mem->name = dev_name(&spi->dev);
 
 	if (IS_ERR_OR_NULL(mem->name))
-		return PTR_ERR(mem->name);
+		return PTR_ERR_OR_ZERO(mem->name);
 
 	spi_set_drvdata(spi, mem);