ACPI / tables: improve comments regarding acpi_parse_entries_array()

I found the description of the table_size argument to the function
acpi_parse_entries_array() unclear and ambiguous.  This is a minor
documentation change to improve that description so I don't misuse
the argument again in the future, and it is hopefully clearer to
other future users.

Signed-off-by: Al Stone <ahs3@redhat.com>
[ rjw: Subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>