package/mraa: disable tests build

mraa build system is looking for a python interpreter >= 2.7 on the host due to
a typo in MRAA_CONF_OPTS. We must use -DBUILDTESTS=OFF instead of -DTESTS=OFF.

Fixes:
http://autobuild.buildroot.net/results/5f0/5f047c4c28b34f6b1bf2306a2b00bcc6a7481c01

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mraa/mraa.mk

@@ -20,6 +20,6 @@ MRAA_CONF_OPTS += \
 	-DIPK=OFF \
 	-DRPM=OFF \
 	-DENABLEEXAMPLES=OFF \
-	-DTESTS=OFF
+	-DBUILDTESTS=OFF
 
 $(eval $(cmake-package))