RISC-V: KVM: Fix riscv_vcpu_get_isa_ext_single() for missing extensions

The riscv_vcpu_get_isa_ext_single() should fail with -ENOENT error
when corresponding ISA extension is not available on the host.

Fixes: e98b108 ("RISC-V: KVM: Factor-out ONE_REG related code to its own source file")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: avpatel

arch/riscv/kvm/vcpu_onereg.c

@@ -460,8 +460,11 @@ static int riscv_vcpu_get_isa_ext_single(struct kvm_vcpu *vcpu,
 	    reg_num >= ARRAY_SIZE(kvm_isa_ext_arr))
 		return -ENOENT;
 
-	*reg_val = 0;
 	host_isa_ext = kvm_isa_ext_arr[reg_num];
+	if (!__riscv_isa_extension_available(NULL, host_isa_ext))
+		return -ENOENT;
+
+	*reg_val = 0;
 	if (__riscv_isa_extension_available(vcpu->arch.isa, host_isa_ext))
 		*reg_val = 1; /* Mark the given extension as available */