RISC-V: KVM: Check kvm_riscv_vcpu_alloc_vector_context() return value

RISC-V: KVM: Check kvm_riscv_vcpu_alloc_vector_context() return value

The kvm_riscv_vcpu_alloc_vector_context() does return an error code
upon failure so don't ignore this in kvm_arch_vcpu_create().

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Nutty Liu <liujingqi@lanxincomputing.com>
Link: https://lore.kernel.org/r/20250618113532.471448-2-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>