aubinator: Store enum textual name in iter->value.

aubinator: Store enum textual name in iter->value.

gen_field_iterator_next() produces a string representing the value of
the field.  For enum values, it also produced a separate "description"
string containing the textual name of the enum.

The only caller of this function combines the two, printing enums as
"<numeric value> (<texture enum name>)".  We may as well just store
that in item->value directly, eliminating the description field, and
a layer of wrapping.

v2: Use non-overlapping source and destination strings in snprintf.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>