ext4: update s_free_{inodes,blocks}_count during online resize

When we're doing an online resize of an ext4 filesystem, we need to
update the free inode and block counts in the superblock so that fsck
doesn't complain.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>