KVM: x86 emulator: fix sparse warnings in x86_emulate.c

Nesting __emulate_2op_nobyte inside__emulate_2op produces many shadowed
variable warnings on the internal variable _tmp used by both macros.

Change the outer macro to use __tmp.

Avoids a sparse warning like the following at every call site of __emulate_2op
arch/x86/kvm/x86_emulate.c:1091:3: warning: symbol '_tmp' shadows an earlier one
arch/x86/kvm/x86_emulate.c:1091:3: originally declared here
[18 more warnings suppressed]

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>