LoongArch: KVM: Remove undefined a6 argument comment for kvm_hypercall()

The kvm_hypercall() set for LoongArch is limited to a1-a5. So the
mention of a6 in the comment is undefined that needs to be rectified.

Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
Signed-off-by: Dandan Zhang <zhangdandan@uniontech.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/kvm_para.h

@@ -39,9 +39,9 @@ struct kvm_steal_time {
  * Hypercall interface for KVM hypervisor
  *
  * a0: function identifier
- * a1-a6: args
+ * a1-a5: args
  * Return value will be placed in a0.
- * Up to 6 arguments are passed in a1, a2, a3, a4, a5, a6.
+ * Up to 5 arguments are passed in a1, a2, a3, a4, a5.
  */
 static __always_inline long kvm_hypercall0(u64 fid)
 {