btrfs: have it use inode_update_timestamps

In later patches, we're going to drop the "now" argument from the
update_time operation. Have btrfs_update_time use the new
inode_update_timestamps helper to fetch a new timestamp and update it
properly.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-Id: <20230807-mgctime-v7-4-d1dec143a704@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/btrfs/inode.c

@@ -6068,14 +6068,7 @@ static int btrfs_update_time(struct inode *inode, struct timespec64 *now,
 	if (btrfs_root_readonly(root))
 		return -EROFS;
 
-	if (flags & S_VERSION)
-		dirty |= inode_maybe_inc_iversion(inode, dirty);
-	if (flags & S_CTIME)
-		inode_set_ctime_to_ts(inode, *now);
-	if (flags & S_MTIME)
-		inode->i_mtime = *now;
-	if (flags & S_ATIME)
-		inode->i_atime = *now;
+	dirty = inode_update_timestamps(inode, flags);
 	return dirty ? btrfs_dirty_inode(BTRFS_I(inode)) : 0;
 }