qextserialport: really disable target (and not staging) install for static builds

Commit f09b33a0a (qextserialport: fix static build) adjusted the logic for
static builds, but the change contained a typo - It disabled
_INSTALL_STAGING for static builds, not _INSTALL_TARGET.

The autobuilders didn't detect this as nothing links against qextserialport
(so the missing staging install didn't cause issues) and the target install
command was only defined for !static.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/qextserialport/qextserialport.mk

@@ -35,7 +35,7 @@ define QEXTSERIALPORT_INSTALL_STAGING_CMDS
 endef
 
 ifeq ($(BR2_STATIC_LIBS),y)
-QEXTSERIALPORT_INSTALL_STAGING = NO
+QEXTSERIALPORT_INSTALL_TARGET = NO
 else
 define QEXTSERIALPORT_INSTALL_TARGET_CMDS
 	cp -a $(@D)/*.so.* $(TARGET_DIR)/usr/lib