powerpc/4xx: Fix return value check in hsta_msi_probe()

In case of error, the function ioremap() returns NULL
not ERR_PTR(). The IS_ERR() test in the return value
check should be replaced with NULL test.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/ppc4xx_hsta_msi.c

@@ -145,7 +145,7 @@ static int hsta_msi_probe(struct platform_device *pdev)
 	ppc4xx_hsta_msi.address = mem->start;
 	ppc4xx_hsta_msi.data = ioremap(mem->start, resource_size(mem));
 	ppc4xx_hsta_msi.irq_count = irq_count;
-	if (IS_ERR(ppc4xx_hsta_msi.data)) {
+	if (!ppc4xx_hsta_msi.data) {
 		dev_err(dev, "Unable to map memory\n");
 		return -ENOMEM;
 	}