KVM: x86/emulator: Fix handing of POP SS to correctly set interruptibility

The emulator checks the wrong variable while setting the CPU
interruptibility state, the target segment is embedded in the instruction
opcode, not the ModR/M register.  Fix the condition.
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Fixes: a5457e7b ("KVM: emulate: POP SS triggers a MOV SS shadow too")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20220821215900.1419215-1-mhal@rbox.coSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/emulate.c

@@ -1953,7 +1953,7 @@ static int em_pop_sreg(struct x86_emulate_ctxt *ctxt)
 	if (rc != X86EMUL_CONTINUE)
 		return rc;
 
-	if (ctxt->modrm_reg == VCPU_SREG_SS)
+	if (seg == VCPU_SREG_SS)
 		ctxt->interruptibility = KVM_X86_SHADOW_INT_MOV_SS;
 	if (ctxt->op_bytes > 2)
 		rsp_increment(ctxt, ctxt->op_bytes - 2);