accel/tcg: Assert noreturn from write-only page for atomics

accel/tcg: Assert noreturn from write-only page for atomics

There should be no "just in case"; the page is already
in the tlb, and known to be not readable.

Reviewed-by: Helge Deller <deller@gmx.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>