package/boost: fix build with python 3.8

Fixes:
 - http://autobuild.buildroot.org/results/81489f92ceb6287a4d6c52b2bb16a80e8c5c430a

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/boost/boost.mk

@@ -67,7 +67,7 @@ ifeq ($(BR2_PACKAGE_BOOST_PYTHON),y)
 BOOST_FLAGS += --with-python-root=$(HOST_DIR)
 ifeq ($(BR2_PACKAGE_PYTHON3),y)
 BOOST_FLAGS += --with-python=$(HOST_DIR)/bin/python$(PYTHON3_VERSION_MAJOR)
-BOOST_TARGET_CXXFLAGS += -I$(STAGING_DIR)/usr/include/python$(PYTHON3_VERSION_MAJOR)m
+BOOST_TARGET_CXXFLAGS += -I$(STAGING_DIR)/usr/include/python$(PYTHON3_VERSION_MAJOR)
 BOOST_DEPENDENCIES += python3
 else
 BOOST_FLAGS += --with-python=$(HOST_DIR)/bin/python$(PYTHON_VERSION_MAJOR)