boost: fix build of context library

Signed-off-by: Patrick Ziegler <patrick.ziegler@fh-kl.de>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/boost/boost.mk

@@ -20,7 +20,7 @@ BOOST_FLAGS =
 BOOST_WITHOUT_FLAGS = python atomic
 
 BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_CHRONO),,chrono)
-BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_CHRONO),,context)
+BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_CONTEXT),,context)
 BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_DATE_TIME),,date_time)
 BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_EXCEPTION),,exception)
 BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_FILESYSTEM),,filesystem)