libmraa: don't set SWIG_DIR

CMake 3.0.12 uses SWIG_DIR to set SWIG_LIB, is used as the library
install location, which defaults to
$(STAGING_HOSTPKG)/share/sig/(SWIGVERSION).  If it is set, then the
installed swig library directory is ignored, and compilation fails:
[ 32%] Swig source
 Error: Unable to find 'swig.swg'
:3: Error: Unable to find 'python.swg'

Instead of setting it manually, let the default be used, which works
well.

Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>

libs/libmraa/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=libmraa
 PKG_VERSION:=0.9.0
 
-PKG_RELEASE=$(PKG_SOURCE_VERSION)
+PKG_RELEASE=$(PKG_SOURCE_VERSION)-1
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://github.com/intel-iot-devkit/mraa.git
@@ -29,8 +29,7 @@ include $(INCLUDE_DIR)/cmake.mk
 
 CMAKE_OPTIONS=-DBUILDARCH=$(CONFIG_ARCH) \
 	-DENABLEEXAMPLES=0 \
-	-DNODE_EXECUTABLE=$(STAGING_DIR_HOSTPKG)/bin/node \
-	-DSWIG_DIR=$(STAGING_DIR_HOSTPKG)/bin
+	-DNODE_EXECUTABLE=$(STAGING_DIR_HOSTPKG)/bin/node
 
 TARGET_CFLAGS+=-I$(STAGING_DIR)/usr/include/node