KVM: x86: cleanup unused local variable

fix:
 arch/x86/kvm/x86.c: In function ‘handle_emulation_failure’:
 arch/x86/kvm/x86.c:3844: warning: unused variable ‘ctxt’

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>