As suggested by shellcheck, stop using expr.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 tools/perf/tests/shell/test_intel_pt.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/perf/tests/shell/test_intel_pt.sh b/tools/perf/tests/shell/test_intel_pt.sh
index 6e40ee7261da..2be8cb03a620 100755
--- a/tools/perf/tests/shell/test_intel_pt.sh
+++ b/tools/perf/tests/shell/test_intel_pt.sh
@@ -64,14 +64,14 @@ test_system_wide_side_band()
 count_result()
 {
 	if [ $1 -eq 2 ] ; then
-		skip_cnt=`expr ${skip_cnt} \+ 1`
+		skip_cnt=$((skip_cnt + 1))
 		return
 	fi
 	if [ $1 -eq 0 ] ; then
-		ok_cnt=`expr ${ok_cnt} \+ 1`
+		ok_cnt=$((ok_cnt + 1))
 		return
 	fi
-	err_cnt=`expr ${err_cnt} \+ 1`
+	err_cnt=$((err_cnt + 1))
 }
 
 test_system_wide_side_band
-- 
2.25.1