cpu-exec: reset BQL after longjmp in cpu_exec_step_atomic

Just like we do in cpu_exec().
Reported-by: NMax Filippov <jcmvbkbc@gmail.com>
Tested-by: NMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

accel/tcg/cpu-exec.c

@@ -266,6 +266,9 @@ void cpu_exec_step_atomic(CPUState *cpu)
 #ifndef CONFIG_SOFTMMU
         tcg_debug_assert(!have_mmap_lock());
 #endif
+        if (qemu_mutex_iothread_locked()) {
+            qemu_mutex_unlock_iothread();
+        }
         assert_no_pages_locked();
     }