firmware: arm_sdei: Fix return value check in sdei_present_dt()

In case of error, the function of_platform_device_create() returns
NULL pointer not ERR_PTR(). The IS_ERR() test in the return value
check should be replaced with NULL test.

Fixes: 677a60bd20 ("firmware: arm_sdei: Discover SDEI support via ACPI")
Acked-by: James Morse <james.morse@arm.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

drivers/firmware/arm_sdei.c

@@ -1023,7 +1023,7 @@ static bool __init sdei_present_dt(void)
 
 	pdev = of_platform_device_create(np, sdei_driver.driver.name, NULL);
 	of_node_put(np);
-	if (IS_ERR(pdev))
+	if (!pdev)
 		return false;
 
 	return true;