cifsd: len can never be negative in ksmbd_init_sg()

Dan pointed out len can not be negative.
This patch remove unneeded negative check in loop.
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifsd/auth.c

@@ -1207,7 +1207,7 @@ static struct scatterlist *ksmbd_init_sg(struct kvec *iov, unsigned int nvec,
 			for (j = 0; j < nr_entries[i]; j++) {
 				unsigned int bytes = PAGE_SIZE - offset;
 
-				if (len <= 0)
+				if (!len)
 					break;
 
 				if (bytes > len)