KVM: arm64: Fix enforcement of upper bound on MDCR_EL2.HPMN

KVM: arm64: Fix enforcement of upper bound on MDCR_EL2.HPMN

Previously, u64_replace_bits() was used to no effect as the return value
was ignored. Convert to u64p_replace_bits() so the value is updated in
place.

Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Fixes: efff9dd2fee7 ("KVM: arm64: Handle out-of-bound write to MDCR_EL2.HPMN")
Link: https://lore.kernel.org/r/20250709093808.920284-2-ben.horgan@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>