perf tests stat+shadow_stat: Fix shellcheck warning about unused variable

Running shellcheck on stat+shadow_stat.sh generates below warning:

In tests/shell/stat+shadow_stat.sh line 48:
        while read cpu num evt hash ipc rest
                               ^--^ SC2034 (warning): hash appears unused. Verify use (or export if used externally).

This variable is intentionally unused since it is needed to parse
through the output. Use "_" as a prefix for this throw away variable.
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230709182800.53002-11-atrajeev@linux.vnet.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/stat+shadow_stat.sh

@@ -14,7 +14,7 @@ test_global_aggr()
 {
 	perf stat -a --no-big-num -e cycles,instructions sleep 1  2>&1 | \
 	grep -e cycles -e instructions | \
-	while read num evt hash ipc rest
+	while read num evt _hash ipc rest
 	do
 		# skip not counted events
 		if [ "$num" = "<not" ]; then
@@ -45,7 +45,7 @@ test_no_aggr()
 {
 	perf stat -a -A --no-big-num -e cycles,instructions sleep 1  2>&1 | \
 	grep ^CPU | \
-	while read cpu num evt hash ipc rest
+	while read cpu num evt _hash ipc rest
 	do
 		# skip not counted events
 		if [ "$num" = "<not" ]; then