package/sox: install to staging

sox also provides one or more libraries with headers, so also install
sox to staging.

Signed-off-by: Adrian Amaglio <nainformatique@gresille.org>
[Giulio: reword commit log]
Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
[yann.morin.1998@free.fr:
  - further refine commit log
  - move assignment in a more sensible location
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/sox/sox.mk

@@ -15,6 +15,7 @@ SOX_CPE_ID_PRODUCT = sound_exchange
 # From git and we're patching configure.ac
 SOX_AUTORECONF = YES
 SOX_AUTORECONF_OPTS = --include=$(HOST_DIR)/share/autoconf-archive
+SOX_INSTALL_STAGING = YES
 
 SOX_IGNORE_CVES += CVE-2017-11332 CVE-2017-11358 CVE-2017-11359 \
 	CVE-2017-15370 CVE-2017-15371 CVE-2017-15372 CVE-2017-15642 \