UPSTREAM: exfat: change to get file size from DataLength

In stream extension directory entry, the ValidDataLength
field describes how far into the data stream user data has
been written, and the DataLength field describes the file
size.

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: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
(cherry picked from commit 11a347fb)

Bug: 362138008

Change-Id: I54ba086dbd80712ded5dea15e394b219400d7fff
Signed-off-by: dongliang.cui <dongliang.cui@unisoc.com>