[NFC][Clang][RISCV] Remove trailing whitespaces in riscv_vector.td

[yronglin]

This whitespaces breaking Format CI.

$ trap 'kill -- $$' INT TERM QUIT; clang/utils/ci/run-buildbot check-format
+ set -o pipefail
+ unset LANG
+ unset LC_ALL
+ unset LC_COLLATE
++ basename clang/utils/ci/run-buildbot
+ PROGNAME=run-buildbot
+ [[ 1 == 0 ]]
+ [[ 1 -gt 0 ]]
+ case ${1} in
+ BUILDER=check-format
+ shift
+ [[ 0 -gt 0 ]]
++ git rev-parse --show-toplevel
+ MONOREPO_ROOT=/var/lib/buildkite-agent/builds/linux-56-fdf668759-vtv88-1/llvm-project/clang-ci
+ BUILD_DIR=/var/lib/buildkite-agent/builds/linux-56-fdf668759-vtv88-1/llvm-project/clang-ci/build/check-format
+ INSTALL_DIR=/var/lib/buildkite-agent/builds/linux-56-fdf668759-vtv88-1/llvm-project/clang-ci/build/check-format/install
+ cmake --version
cmake version 3.23.3
CMake suite maintained and supported by Kitware (kitware.com/cmake).
+ ninja --version
1.10.1
+ case "${BUILDER}" in
+ grep -rnI '[[:blank:]]$' clang/lib clang/include clang/docs
clang/include/clang/Basic/riscv_vector.td:580:        let Name = op # eew # "_v", IRName = op, MaskedIRName = op # "_mask",
clang/include/clang/Basic/riscv_vector.td:1786:    let RequiredFeatures = ["ZvfhminOrZvfh"] in

[kito-cheng]

LGTM

[yronglin]

Thanks for the review! @kito-cheng