package/opencv3: fix typo in OPENCV_WARNINGS_ARE_ERRORS

OPENCV3_WARNINGS_ARE_ERRORS option does not exist so rename it to
OPENCV_WARNINGS_ARE_ERRORS (even if it is already disabled by default)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/opencv3/opencv3.mk

@@ -53,7 +53,7 @@ OPENCV3_CONF_OPTS += \
 	-DENABLE_OMIT_FRAME_POINTER=ON \
 	-DENABLE_PRECOMPILED_HEADERS=OFF \
 	-DENABLE_PROFILING=OFF \
-	-DOPENCV3_WARNINGS_ARE_ERRORS=OFF
+	-DOPENCV_WARNINGS_ARE_ERRORS=OFF
 
 # OpenCV link options
 OPENCV3_CONF_OPTS += \