package/kf5-kcoreaddons: fix check-package warnings

KF5_KCOREADDONS_CONF_OPTS is set both outside and inside the
conditional block, so the value set outside would be lost if
the condition were to be true.

Use append-assignement in this case, as reported by check-package.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit f7e750e8f514f84bf2f4fc99976dd11f19c8ecbc)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/kf5/kf5-kcoreaddons/kf5-kcoreaddons.mk

@@ -23,7 +23,7 @@ KF5_KCOREADDONS_CONF_OPTS = -DCMAKE_CXX_FLAGS="$(KF5_KCOREADDONS_CXXFLAGS)"
 
 ifeq ($(BR2_microblaze),y)
 # Microblaze ld emits warnings, make warnings not to be treated as errors
-KF5_KCOREADDONS_CONF_OPTS = -DCMAKE_SHARED_LINKER_FLAGS="-Wl,--no-fatal-warnings"
+KF5_KCOREADDONS_CONF_OPTS += -DCMAKE_SHARED_LINKER_FLAGS="-Wl,--no-fatal-warnings"
 endif
 
 $(eval $(cmake-package))