ksmbd: change data type of volatile/persistent id to u64

This patch change data type of volatile/persistent id to u64 to make
issue from idr_find and idr_remove(). !HAS_FILE_ID check will protect
integer overflow issue from idr_find and idr_remove().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>