libsecret: specify where libgcrypt lives

When libgcrypt support is enabled the configure script will try to
find libgcrypt-config in the PATH. If the host distribution has it then
brokeness ensues. Fixes:
http://autobuild.buildroot.net/results/eca/eca10b8360354e7e51406f7ac942d343987bde5e/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libsecret/libsecret.mk

@@ -16,7 +16,8 @@ LIBSECRET_CONF_OPT = --disable-manpages --disable-strict --disable-coverage --en
 
 ifeq ($(BR2_PACKAGE_LIBGCRYPT),y)
 	LIBSECRET_DEPENDENCIES += libgcrypt
-	LIBSECRET_CONF_OPT += --enable-gcrypt
+	LIBSECRET_CONF_OPT += --enable-gcrypt \
+		--with-libgcrypt-prefix=$(STAGING_DIR)/usr
 else
 	LIBSECRET_CONF_OPT += --disable-gcrypt
 endif