ACPI: NUMA: Remove the useless sub table pointer check

In acpi_parse_entries_array(), the subtable entries (entry.hdr)
will never be NULL, so for ACPI subtable handler in struct
acpi_subtable_proc, will never handle NULL subtable entries.

Remove those useless subtable pointer checks in the callback
handlers.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>