ext4: move i_size,i_disksize update routines to helper function

Cc: stable@vger.kernel.org # needed for bug fix patches
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --cc fs/ext4/ext4.h
Simple merge

diff --cc fs/ext4/extents.c
Simple merge

diff --cc fs/ext4/inode.c
Simple merge