octeontx2-af: npc: cn20k: Fix subbank free list indexing for search order

octeontx2-af: npc: cn20k: Fix subbank free list indexing for search order

subbank_srch_order[i] is the physical subbank at search-order slot i,
so each subbank's arr_idx must be i (its slot), not
subbank_srch_order[sb->idx].  The old logic mis-keyed xa_sb_free
and broke allocation traversal order.

Populate arr_idx and xa_sb_free in a single pass over the search
order after subbank structs are initialized.

Fixes: 7ac9d4c4075c ("octeontx2-af: npc: cn20k: add subbank search order control")
Signed-off-by: Ratheesh Kannoth <rkannoth@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260619095100.1864440-1-rkannoth@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>