CIFS: Use memdup_user() rather than duplicating its implementation

Reuse existing functionality from memdup_user() instead of keeping
duplicate source code.

Generated by: scripts/coccinelle/api/memdup_user.cocci

Fixes: f5b05d62

 ("cifs: add IOCTL for QUERY_INFO passthrough to userspace")
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Steve French <stfrench@microsoft.com>