KVM: arm64: Remove dead PMU sysreg decoding code

The handling of traps in access_pmu_evcntr() has a couple of
omminous "else return false;" statements that don't make any sense:
the decoding tree coverse all the registers that trap to this handler,
and returning false implies that we change PC, which we don't.

Get rid of what is evidently dead code.

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/sys_regs.c

@@ -717,7 +717,7 @@ static bool access_pmu_evcntr(struct kvm_vcpu *vcpu,
 			      struct sys_reg_params *p,
 			      const struct sys_reg_desc *r)
 {
-	u64 idx;
+	u64 idx = ~0UL;
 
 	if (r->CRn == 9 && r->CRm == 13) {
 		if (r->Op2 == 2) {
@@ -733,8 +733,6 @@ static bool access_pmu_evcntr(struct kvm_vcpu *vcpu,
 				return false;
 
 			idx = ARMV8_PMU_CYCLE_IDX;
-		} else {
-			return false;
 		}
 	} else if (r->CRn == 0 && r->CRm == 9) {
 		/* PMCCNTR */
@@ -748,10 +746,11 @@ static bool access_pmu_evcntr(struct kvm_vcpu *vcpu,
 			return false;
 
 		idx = ((r->CRm & 3) << 3) | (r->Op2 & 7);
-	} else {
-		return false;
 	}
 
+	/* Catch any decoding mistake */
+	WARN_ON(idx == ~0UL);
+
 	if (!pmu_counter_idx_valid(vcpu, idx))
 		return false;