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: adf617210596 ("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>