ACPI / memhotplug: Fix a stale pointer in error path

device->driver_data needs to be cleared when releasing its data,
mem_device, in an error path of acpi_memory_device_add().

The function evaluates the _CRS of memory device objects, and fails
when it gets an unexpected resource or cannot allocate memory. A
kernel crash or data corruption may occur when the kernel accesses
the stale pointer.

Signed-off-by: Toshi Kani <[e-mail]>
Reviewed-by: Yasuaki Ishimatsu <[e-mail]>
Cc: 2.6.32+ <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/acpi_memhotplug.c

···
 	/* Get the range from the _CRS */
 	result = acpi_memory_get_device_resources(mem_device);
 	if (result) {
+		device->driver_data = NULL;
 		kfree(mem_device);
 		return result;
 	}