UPSTREAM: exfat: do not zero the extended part

Since the read operation beyond the ValidDataLength returns zero,
if we just extend the size of the file, we don't need to zero the
extended part, but only change the DataLength without changing
the ValidDataLength.

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 f55c096f)

Bug: 362138008

Change-Id: Ic51c9d6516ba259ab7aacb35c6b0cedba26c8e74
Signed-off-by: dongliang.cui <dongliang.cui@unisoc.com>