build: Makefile: remove bashism

Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com>
diff --git a/tests/Makefile b/tests/Makefile
index f83d186..e33fe52 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -433,7 +433,7 @@
 		RESULT=`$(CHECK_PRELOAD) ./$${i} | grep -v 'PASS$$' | grep -v -- '----' | grep -v '^$$'`;	\
 		PASSED=`echo $$RESULT |grep PASSED`; 								\
 		echo "   $$RESULT";													\
-		if [ "$$PASSED" == "" ];											\
+		if [ "$$PASSED" = "" ];											\
 		then																\
 			echo "**** Failed ***************";								\
 			RETURN=1;														\