RISC-V: KVM: Fix incorrect reg_subtype labels in kvm_riscv_vcpu_set_reg_isa_ext function

In the function kvm_riscv_vcpu_set_reg_isa_ext, the original code
used incorrect reg_subtype labels KVM_REG_RISCV_SBI_MULTI_EN/DIS.
These have been corrected to KVM_REG_RISCV_ISA_MULTI_EN/DIS respectively.
Although they are numerically equivalent, the actual processing
will not result in errors, but it may lead to ambiguous code semantics.

Fixes: 61302944

 ("RISC-V: KVM: Extend ONE_REG to enable/disable multiple ISA extensions")
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/ff1c6771a67d660db94372ac9aaa40f51e5e0090.1716429371.git.zhouquan@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>