package/libopenmpt: install to staging to fix pkg-config

Without this, packages using libopenmpt are not able to find
the dependency.

Signed-off-by: J. Neuschäfer <j.neuschaefer@gmx.net>
[Julien: reword commit log]
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/libopenmpt/libopenmpt.mk

@@ -11,6 +11,7 @@ LIBOPENMPT_LICENSE = BSD-3-Clause
 LIBOPENMPT_LICENSE_FILES = LICENSE
 LIBOPENMPT_CPE_ID_VENDOR = openmpt
 LIBOPENMPT_DEPENDENCIES = host-pkgconf
+LIBOPENMPT_INSTALL_STAGING = YES
 
 ifeq ($(BR2_PACKAGE_LIBOPENMPT_OPENMPT123),y)
 LIBOPENMPT_CONF_OPTS += --enable-openmpt123