mm: vmscan: modify an easily misunderstood function name

When looking at the code in the memory part, I found that the purpose of
the function prepare_scan_countis very different from the function name. 
It is easy to misunderstand when reading.The function prepare_scan_count
mainly completes the assignment of the scan_control structure.Therefore, I
suggest that the function name can be changed to prepare_scan_control,
which is easier to understand.

Link: https://lkml.kernel.org/r/20230912085923.27238-1-liujinlong@kylinos.cn


Signed-off-by: liujinlong <liujinlong@kylinos.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>