RISC-V: KVM: No need to use mask when hart-index-bit is 0

RISC-V: KVM: No need to use mask when hart-index-bit is 0

When the maximum hart number within groups is 1, hart-index-bit is set to
0. Consequently, there is no need to restore the hart ID from IMSIC
addresses and hart-index-bit settings. Currently, QEMU and kvmtool do not
pass correct hart-index-bit values when the maximum hart number is a
power of 2, thereby avoiding this issue. Corresponding patches for QEMU
and kvmtool will also be dispatched.

Fixes: 89d01306e34d ("RISC-V: KVM: Implement device interface for AIA irqchip")
Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20240415064905.25184-1-yongxuan.wang@sifive.com
Signed-off-by: Anup Patel <anup@brainfault.org>