ARM: mvebu: Fix kernel hang in mvebu_soc_id_init() when of_iomap failed

When pci_base is accessed whereas it has not been properly mapped by
of_iomap() the kernel hang. The check of this pointer made an improper
use of IS_ERR() instead of comparing to NULL. This patch fix this
issue.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Reported-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Cc: stable@vger.kernel.org # v3.12+: af8d1c63afcb: ARM: mvebu: Add support to get the ID and the revision of a SoC
Cc: stable@vger.kernel.org # v3.12+: 85e618a1be2b: ARM: mvebu: Add quirk for i2c for the OpenBlocks AX3-4 board
Cc: stable@vger.kernel.org # v3.12+: 6cf70ae928ba: i2c: mv64xxx: Fix bus hang on A0 version of the Armada XP SoCs
Cc: stable@vger.kernel.org # v3.12+: f8b94beb7e6a: i2c: mv64xxx: Document the newly introduced Armada XP A0 compatible
Cc: stable@vger.kernel.org # v3.12+
Fixes: 930ab3d403ae (i2c: mv64xxx: Add I2C Transaction Generator support)
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

arch/arm/mach-mvebu/mvebu-soc-id.c

@@ -88,7 +88,7 @@ static int __init mvebu_soc_id_init(void)
 	}
 
 	pci_base = of_iomap(child, 0);
-	if (IS_ERR(pci_base)) {
+	if (pci_base == NULL) {
 		pr_err("cannot map registers\n");
 		ret = -ENOMEM;
 		goto res_ioremap;