fs/ntfs3: Harden against integer overflows

Smatch complains that the "add_bytes" is not to be trusted.  Use
size_add() to prevent an integer overflow.

Fixes: be71b5cb ("fs/ntfs3: Add attrib operations")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>