tcg: Really fix cpu_io_recompile

We have confused the number of instructions that have been
executed in the TB with the number of instructions needed
to repeat the I/O instruction.

We have used cpu_restore_state_from_tb, which means that
the guest pc is pointing to the I/O instruction.  The only
time the answer to the later question is not 1 is when
MIPS or SH4 need to re-execute the branch for the delay
slot as well.

We must rely on cpu->cflags_next_tb to generate the next TB,
as otherwise we have a race condition with other guest cpus
within the TB cache.

Fixes: 0790f868
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180319031545.29359-1-richard.henderson@linaro.org>
Tested-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>