RISC-V: KVM: set 'vlenb' in kvm_riscv_vcpu_alloc_vector_context()

'vlenb', added to riscv_v_ext_state by commit c35f3aa3 ("RISC-V:
vector: export VLENB csr in __sc_riscv_v_state"), isn't being
initialized in guest_context. If we export 'vlenb' as a KVM CSR,
something we want to do in the next patch, it'll always return 0.

Set 'vlenb' to riscv_v_size/32.
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/vcpu_vector.c

@@ -76,6 +76,7 @@ int kvm_riscv_vcpu_alloc_vector_context(struct kvm_vcpu *vcpu,
 	cntx->vector.datap = kmalloc(riscv_v_vsize, GFP_KERNEL);
 	if (!cntx->vector.datap)
 		return -ENOMEM;
+	cntx->vector.vlenb = riscv_v_vsize / 32;
 
 	vcpu->arch.host_context.vector.datap = kzalloc(riscv_v_vsize, GFP_KERNEL);
 	if (!vcpu->arch.host_context.vector.datap)