LoongArch: KVM: Fix base address calculation in kvm_eiointc_regs_access()

LoongArch: KVM: Fix base address calculation in kvm_eiointc_regs_access()

In function kvm_eiointc_regs_access(), the register base address is
caculated from array base address plus offset, the offset is absolute
value from the base address. The data type of array base address is
u64, it should be converted into the "void *" type and then plus the
offset.

Cc: <stable@vger.kernel.org>
Fixes: d3e43a1f34ac ("LoongArch: KVM: Use 64-bit register definition for EIOINTC").
Reported-by: Aurelien Jarno <aurel32@debian.org>
Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1131431
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>