qextserialport: define QEXTSERIALPORT_CONFIGURE_CMDS only once

Distinguish qt/qt5 by defining QEXTSERIALPORT_QMAKE, like is done e.g.
for quazip.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/qextserialport/qextserialport.mk

@@ -12,15 +12,15 @@ QEXTSERIALPORT_INSTALL_STAGING = YES
 
 ifeq ($(BR2_PACKAGE_QT),y)
 QEXTSERIALPORT_DEPENDENCIES += qt
-define QEXTSERIALPORT_CONFIGURE_CMDS
-	(cd $(@D); $(TARGET_MAKE_ENV) $(QT_QMAKE))
-endef
+QEXTSERIALPORT_QMAKE = $(QT_QMAKE)
 else ifeq ($(BR2_PACKAGE_QT5),y)
 QEXTSERIALPORT_DEPENDENCIES += qt5base
+QEXTSERIALPORT_QMAKE = $(QT5_QMAKE)
+endif
+
 define QEXTSERIALPORT_CONFIGURE_CMDS
-	(cd $(@D); $(TARGET_MAKE_ENV) $(QT5_QMAKE))
+	(cd $(@D); $(TARGET_MAKE_ENV) $(QEXTSERIALPORT_QMAKE))
 endef
-endif
 
 define QEXTSERIALPORT_BUILD_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D)