exfat: remove duplicate write inode for truncating file

This commit moves updating file attributes and timestamps before
calling __exfat_write_inode(), so that all updates of the inode
had been written by __exfat_write_inode(), mark_inode_dirty() is
unneeded.

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Reviewed-by: Andy Wu <Andy.Wu@sony.com>
Reviewed-by: Aoyama Wataru <wataru.aoyama@sony.com>
Reviewed-by: Daniel Palmer <daniel.palmer@sony.com>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>