[MINOR] Only rename SparkR tar.gz if names mismatch

## What changes were proposed in this pull request?

For release builds the R_PACKAGE_VERSION and VERSION are the same (e.g., 2.1.0). Thus `cp` throws an error which causes the build to fail.

## How was this patch tested?

Manually by executing the following script
```
set -o pipefail
set -e
set -x

touch a

R_PACKAGE_VERSION=2.1.0
VERSION=2.1.0

if [ "$R_PACKAGE_VERSION" != "$VERSION" ]; then
  cp a a
fi
```

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes apache#16299 from shivaram/sparkr-cp-fix.

dev/make-distribution.sh

@@ -228,8 +228,8 @@ if [ "$MAKE_R" == "true" ]; then
   # Install source package to get it to generate vignettes, etc.
   # Do not source the check-cran.sh - it should be run from where it is for it to set SPARK_HOME
   NO_TESTS=1 CLEAN_INSTALL=1 "$SPARK_HOME/"R/check-cran.sh
-  # Make a copy of R source package matching the Spark release version.
-  cp $SPARK_HOME/R/SparkR_"$R_PACKAGE_VERSION".tar.gz $SPARK_HOME/R/SparkR_"$VERSION".tar.gz
+  # Move R source package to file name matching the Spark release version.
+  mv $SPARK_HOME/R/SparkR_"$R_PACKAGE_VERSION".tar.gz $SPARK_HOME/R/SparkR_"$VERSION".tar.gz
   popd > /dev/null
 else
   echo "Skipping building R source package"