[SPARK-16035][PYSPARK] Fix SparseVector parser assertion for end parenthesis
[SPARK-16035][PYSPARK] Fix SparseVector parser assertion for end parenthesis

## What changes were proposed in this pull request?
The check on the end parenthesis of the expression to parse was using the wrong variable. I corrected that.
## How was this patch tested?
Manual test

Author: andreapasqua <andrea@radius.com>

Closes #13750 from andreapasqua/sparse-vector-parser-assertion-fix.

(cherry picked from commit 4c64e88d5ba4c36cbdbc903376492f0f43401e4e)
Signed-off-by: Xiangrui Meng <9616cf314f60cbadfd3d5d51110130ad7923defb@databricks.com>

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