selftests: ktap_helpers: Make it POSIX-compliant

There are a couple uses of bash specific syntax in the script. Change
them to the equivalent POSIX syntax. This doesn't change functionality
and allows non-bash test scripts to make use of these helpers.
Reported-by: Mike Looijmans <mike.looijmans@topic.nl>
Closes: https://lore.kernel.org/all/efae4037-c22a-40be-8ba9-7c1c12ece042@topic.nl/
Fixes: 2dd0b5a8 ("selftests: ktap_helpers: Add a helper to finish the test")
Fixes: 14571ab1 ("kselftest: Add new test for detecting unprobed Devicetree devices")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/kselftest/ktap_helpers.sh

@@ -43,7 +43,7 @@ __ktap_test() {
 	directive="$3" # optional
 
 	local directive_str=
-	[[ ! -z "$directive" ]] && directive_str="# $directive"
+	[ ! -z "$directive" ] && directive_str="# $directive"
 
 	echo $result $KTAP_TESTNO $description $directive_str
 
@@ -99,7 +99,7 @@ ktap_exit_fail_msg() {
 ktap_finished() {
 	ktap_print_totals
 
-	if [ $(("$KTAP_CNT_PASS" + "$KTAP_CNT_SKIP")) -eq "$KSFT_NUM_TESTS" ]; then
+	if [ $((KTAP_CNT_PASS + KTAP_CNT_SKIP)) -eq "$KSFT_NUM_TESTS" ]; then
 		exit "$KSFT_PASS"
 	else
 		exit "$KSFT_FAIL"