dm snapshot: use true/false for bool variable

Fixes coccicheck warning:

drivers/md/dm-snap.c:1064:3-18: WARNING: Assignment of 0/1 to bool variable
drivers/md/dm-snap.c:1152:1-16: WARNING: Assignment of 0/1 to bool variable
drivers/md/dm-snap.c:1317:1-16: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-snap.c

@@ -1061,7 +1061,7 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
 			DMERR("Read error in exception store: "
 			      "shutting down merge");
 			down_write(&s->lock);
-			s->merge_failed = 1;
+			s->merge_failed = true;
 			up_write(&s->lock);
 		}
 		goto shut;
@@ -1149,7 +1149,7 @@ static void merge_callback(int read_err, unsigned long write_err, void *context)
 
 shut:
 	down_write(&s->lock);
-	s->merge_failed = 1;
+	s->merge_failed = true;
 	b = __release_queued_bios_after_merge(s);
 	up_write(&s->lock);
 	error_bios(b);
@@ -1314,7 +1314,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	INIT_LIST_HEAD(&s->list);
 	spin_lock_init(&s->pe_lock);
 	s->state_bits = 0;
-	s->merge_failed = 0;
+	s->merge_failed = false;
 	s->first_merging_chunk = 0;
 	s->num_merging_chunks = 0;
 	bio_list_init(&s->bios_queued_during_merge);