target/i386/hvf: Use x86_cpu in simulate_[rdmsr|wrmsr]()

target/i386/hvf: Use x86_cpu in simulate_[rdmsr|wrmsr]()

We already have 'x86_cpu = X86_CPU(cpu)'. Use the variable
instead of doing another QOM cast with X86_CPU().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Roman Bolshakov <roman@roolebo.dev>
Tested-by: Roman Bolshakov <roman@roolebo.dev>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Message-Id: <20231009110239.66778-6-philmd@linaro.org>