ksm: initialize the addr only once in rmap_walk_ksm

ksm: initialize the addr only once in rmap_walk_ksm

This is a minor performance optimization, especially when there are many
for-loop iterations, because the addr variable doesn't change across
iterations.

Therefore, it only needs to be initialized once before the loop.

Link: https://lkml.kernel.org/r/20260212192820223O_r2NQzSEPG_C56cs-z4l@zte.com.cn
Link: https://lkml.kernel.org/r/20260212192932941MSsJEAyoRW4YdLBN7_myn@zte.com.cn
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Hugh Dickins <hughd@google.com>
Cc: Wang Yaxin <wang.yaxin@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>