memory: jz4780_nemc: Fix an error pointer vs NULL check in probe()

The devm_ioremap() function returns NULL on error, it doesn't return
error pointers.  This bug could lead to an Oops during probe.

Fixes: f046e4a3 ("memory: jz4780_nemc: Only request IO memory the driver will use")
Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200803143607.GC346925@mwandaSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

drivers/memory/jz4780-nemc.c

@@ -304,9 +304,9 @@ static int jz4780_nemc_probe(struct platform_device *pdev)
 	}
 
 	nemc->base = devm_ioremap(dev, res->start, NEMC_REG_LEN);
-	if (IS_ERR(nemc->base)) {
+	if (!nemc->base) {
 		dev_err(dev, "failed to get I/O memory\n");
-		return PTR_ERR(nemc->base);
+		return -ENOMEM;
 	}
 
 	writel(0, nemc->base + NEMC_NFCSR);