RISC-V: KVM: Fix skip of valid pages in kvm_riscv_gstage_unmap_range

RISC-V: KVM: Fix skip of valid pages in kvm_riscv_gstage_unmap_range

Same as kvm_riscv_gstage_wp_range, the possible valid pages should not
be skipped if !found_leaf. Different from wp case, which can
write-protect more than asked, unmap can't do that, no splitting is
added right now but a warning is logged instead.

Signed-off-by: Wu Fei <wu.fei9@sanechips.com.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260604230317.30501-3-atwufei@163.com
Signed-off-by: Anup Patel <anup@brainfault.org>