too_many_isolated() should return bool as does the similar
too_many_isolated() in mm/compaction.c.

Link: https://lkml.kernel.org/r/20240205042618.108140-1-gehao@kylinos.cnSigned-off-by: Hao Ge <gehao@kylinos.cn>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>