mm/page_ext: remove unused return value of offline_page_ext

Patch series "minor cleanups for page_ext".

This series contains some random minor cleanups for page_ext.  More
details can be found in respective patches.  


This patch (of 3):

offline_page_ext always returns 0 and no caller checks the return value. 
Just remove unused return value of offline_page_ext.

Link: https://lkml.kernel.org/r/20230714114749.1743032-1-shikemeng@huaweicloud.com
Link: https://lkml.kernel.org/r/20230714114749.1743032-2-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>