tcg: Remove unneeded assertion

Commit 7f6f0ae5b95adfa76e10eabe2c34424a955fd10c added two assertions.

One of these assertions is not needed:
The pointer ts is never NULL because it is initialized with the
address of an array element.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
