tools/gpio: Enable compiler optimization to catch more bugs

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/tools/gpio/Makefile b/tools/gpio/Makefile
index 4d198d5..c155d6b 100644
--- a/tools/gpio/Makefile
+++ b/tools/gpio/Makefile
@@ -1,5 +1,5 @@
 CC = $(CROSS_COMPILE)gcc
-CFLAGS += -Wall -g -D_GNU_SOURCE
+CFLAGS += -O2 -Wall -g -D_GNU_SOURCE
 
 all: lsgpio