libext2fs: update i_size in ext2fs_file_write()

libext2fs: update i_size in ext2fs_file_write()

ext2fs_file_write() needs to update i_size on successful write,
otherwise, ext2fs_file_read() in same open/close cycle will not
be able to read the just written data.

This fixes a bug which results in the the problem of quotacheck
triggered on 'tune2fs -O quota' failed to write back multiple
users/groups accounting information.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>