accel/tcg: Fix atomic_mmu_lookup vs TLB_FORCE_SLOW

accel/tcg: Fix atomic_mmu_lookup vs TLB_FORCE_SLOW

When we moved TLB_MMIO and TLB_DISCARD_WRITE to TLB_SLOW_FLAGS_MASK,
we failed to update atomic_mmu_lookup to properly reconstruct flags.

Fixes: 24b5e0fdb543 ("include/exec: Move TLB_MMIO, TLB_DISCARD_WRITE to slow flags")
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>