KVM: selftests: Change MDSCR_EL1 register holding variables as uint64_t

KVM: selftests: Change MDSCR_EL1 register holding variables as uint64_t

Change MDSCR_EL1 register holding local variables as uint64_t that reflects
its true register width as well.

Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: kvm@vger.kernel.org
Cc: kvmarm@lists.linux.dev
Cc: linux-kernel@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250613023646.1215700-3-anshuman.khandual@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>