platform/x86: dell-laptop: fix error return code in dell_init()

Fix to return error code -ENOMEM from the kzalloc() error handling
case instead of 0, as done elsewhere in this function.

Fixes: 549b4930

 ("platform/x86: dell-smbios: Introduce dispatcher for SMM calls")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>