mm/shmem: remove unused entry_order after large swapin rework

mm/shmem: remove unused entry_order after large swapin rework

After commit 93c0476e7057 ("mm/shmem, swap: rework swap entry and index
calculation for large swapin"), xas_get_order() will never return a
non-zero value for `entry_order` in shmem_split_large_entry().  As a
result, the local variable `entry_order` is effectively unused.

Clean up the code by removing `entry_order` and directly using
`cur_order`.  This change is purely a refactor and has no functional
impact.

No functional change intended.

Link: https://lkml.kernel.org/r/20250908062614.89880-1-liu.yun@linux.dev
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>