fat: (exportfs) move code to rebuild directory-inode to separate function

fat: (exportfs) move code to rebuild directory-inode to separate function

Move the logic to rebuild directory inode (when mounted with nostale_ro)
to new function fat_rebuild_parent()

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>