writeback: fix call of incorrect macro

writeback: fix call of incorrect macro

 the variable 'history' is of type u16, it may be an error
 that the hweight32 macro was used for it
 I guess macro hweight16 should be used

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 2a81490811d0 ("writeback: implement foreign cgroup inode detection")
Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230119104443.3002-1-korotkov.maxim.s@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>