Fix run_tpcds data dir

[gabotechs]

Which issue does this PR close?

• Closes #.

Rationale for this change

Running ./bench.sh run tpcds with a freshly created ./bench.sh data tpcds fails with the following error:

Please prepare TPC-DS data first by following instructions:
  ./bench.sh data tpcds

This PR fixes it

What changes are included in this PR?

Fixes the TPCDS_DIR variable in run_tpcds

Are these changes tested?

just benchmark scripts

Are there any user-facing changes?

no need

[comphead]

Thanks @gabotechs I think it shouldn't be there. by default the script checks for datafusion-benchmarks repo here https://github.com/apache/datafusion-benchmarks/tree/main/tpcds/data/sf1 and there is no tpcds-sf1.

you can specify your own DATA_DIR like

export DATA_DIR=../../datafusion-benchmarks/tpcds/data/sf1/
and then run tpcds benchmarks

[gabotechs]

🤔 Are you sure? I get the impression that this is why the benchmark run commands are failing

#19761 (comment)

Also, note how the data_tpcds() function counterpart actually has this same line:

https://github.com/apache/datafusion/blob/main/benchmarks/bench.sh#L633

# Downloads TPC-DS data
data_tpcds() {
    TPCDS_DIR="${DATA_DIR}/tpcds_sf1"