riscv64: Use `Stored()` insted of `Sd()` as the offset is too large.

Using `Sd()` triggered debug check failure in 597-deopt-busy-loop:
    `assembler_riscv64.h:2403 Check failed: IsInt<12>(imm12) 2616`

Test: 597-deopt-busy-loop passed in debug mode:
    export SOONG_ALLOW_MISSING_DEPENDENCIES=true
    export ART_TEST_SSH_USER=ubuntu
    export ART_TEST_SSH_HOST=localhost
    export ART_TEST_SSH_PORT=10002
    export ART_TEST_ON_VM=true

    . ./build/envsetup.sh
    lunch riscv64-trunk_staging-eng
    art/tools/buildbot-build.sh --target -j72 #--installclean

    . art/tools/buildbot-utils.sh
    art/tools/buildbot-cleanup-device.sh
    art/tools/buildbot-setup-device.sh
    art/tools/buildbot-sync.sh

    art/test/run-test --chroot $ART_TEST_CHROOT \
        --64 --optimizing 597-deopt-busy-loop

Change-Id: I30f4b90ac3b041d713960411e6670f4129beadf9