intel/genxml: Fix comparing xml when node counts differ

intel/genxml: Fix comparing xml when node counts differ

This fix is more relevant to MR !20593. Normally when sorting the
number of nodes will be equivalent today, so this bug will not be
encountered. But in !20593, we can shrink (--import) or grow the
number of elements (--flatten) when the genxml_import.py tool is used.

Fixes: e60a0b16163 ("intel/genxml: Move sorting & writing into GenXml class")
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24902>