dm: convert ffs to __ffs

ffs counts bit starting with 1 (for the least significant bit), __ffs
counts bits starting with 0. This patch changes various occurrences of ffs
to __ffs and removes subtraction of 1 from the result.

Note that __ffs (unlike ffs) is not defined when called with zero
argument, but it is not called with zero argument in any of these cases.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c
index 1ffbeb1..28d4586 100644
--- a/drivers/md/dm-cache-policy-smq.c
+++ b/drivers/md/dm-cache-policy-smq.c
@@ -566,7 +566,7 @@
 
 	ht->es = es;
 	nr_buckets = roundup_pow_of_two(max(nr_entries / 4u, 16u));
-	ht->hash_bits = ffs(nr_buckets) - 1;
+	ht->hash_bits = __ffs(nr_buckets);
 
 	ht->buckets = vmalloc(sizeof(*ht->buckets) * nr_buckets);
 	if (!ht->buckets)