ACPI, APEI, Fix APEI related table size checking

On Huang Ying's machine:

erst_tab->header_length == sizeof(struct acpi_table_einj)

but Yinghai reported that on his machine,

erst_tab->header_length == sizeof(struct acpi_table_einj) -
sizeof(struct acpi_table_header)

To make erst table size checking code works on all systems, both
testing are treated as PASS.

Same situation applies to einj_tab->header_length, so corresponding
table size checking is changed in similar way too.

v2:

- Treat both table size as valid

Originally-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>