btrfs: switch extent_buffer write_locks from atomic to int

The write_locks is either 0 or 1 and always updated under the lock,
so we don't need the atomic_t semantics.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index fef346c..464e6b7 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4879,7 +4879,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
 	eb->spinning_writers = 0;
 	atomic_set(&eb->spinning_readers, 0);
 	atomic_set(&eb->read_locks, 0);
-	atomic_set(&eb->write_locks, 0);
+	eb->write_locks = 0;
 #endif
 
 	return eb;