ACPI, APEI, EINJ: Fix error return code in einj_init()

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

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Chen Gong <gong.chen@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>