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>

accel/tcg/cputlb.c

@@ -1852,10 +1852,9 @@ static void *atomic_mmu_lookup(CPUState *cpu, vaddr addr, MemOpIdx oi,
         /*
          * Since we don't support reads and writes to different
          * addresses, and we do have the proper page loaded for
-         * write, this shouldn't ever return.  But just in case,
-         * handle via stop-the-world.
+         * write, this shouldn't ever return.
          */
-        goto stop_the_world;
+        g_assert_not_reached();
     }
     /* Collect tlb flags for read. */
     tlb_addr |= tlbe->addr_read;