cmake: Use namespaced greentea client library

When using an exported or installed version of greentea, it's necessary
to use the greentea namespace.

Author: Patater

tools/cmake/mbed_greentea.cmake

@@ -60,9 +60,9 @@ macro(mbed_greentea_add_test)
     #    -D "MBED_TEST_LINK_LIBRARIES=mbed-baremetal ext-errorlogging"
     if (DEFINED MBED_TEST_LINK_LIBRARIES)
         separate_arguments(MBED_TEST_LINK_LIBRARIES)
-        list(APPEND MBED_GREENTEA_TEST_REQUIRED_LIBS ${MBED_TEST_LINK_LIBRARIES} greentea-client mbed-unity mbed-utest)
+        list(APPEND MBED_GREENTEA_TEST_REQUIRED_LIBS ${MBED_TEST_LINK_LIBRARIES} greentea::client mbed-unity mbed-utest)
     else()
-        list(APPEND MBED_GREENTEA_TEST_REQUIRED_LIBS greentea-client mbed-unity mbed-utest)
+        list(APPEND MBED_GREENTEA_TEST_REQUIRED_LIBS greentea::client mbed-unity mbed-utest)
     endif()
 
     target_link_libraries(${MBED_GREENTEA_TEST_NAME}