mm/hugetlb: fix early boot crash on parameters without '=' separator

In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix early boot crash on parameters without '=' separator If hugepages, hugepagesz, or default_hugepagesz are specified on the kernel command line without the '=' separator, early parameter parsing passes NULL to hugetlb_add_param(), which dereferences it in strlen() and can crash the system during early boot. Reject NULL values in hugetlb_add_param() and return -EINVAL instead.