irqchip/riscv-aplic: Fix an IS_ERR() vs NULL bug in probe()

The devm_platform_ioremap_resource() function doesn't return NULL, it
returns error pointers.  Fix the error handling to match.

Fixes: 2333df5 ("irqchip: Add RISC-V advanced PLIC driver for direct-mode")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/a5a628d6-81d8-4933-81a8-64aad4743ec4@stanley.mountain

Author: Dan Carpenter

drivers/irqchip/irq-riscv-aplic-main.c

@@ -175,9 +175,9 @@ static int aplic_probe(struct platform_device *pdev)
 
 	/* Map the MMIO registers */
 	regs = devm_platform_ioremap_resource(pdev, 0);
-	if (!regs) {
+	if (IS_ERR(regs)) {
 		dev_err(dev, "failed map MMIO registers\n");
-		return -ENOMEM;
+		return PTR_ERR(regs);
 	}
 
 	/*