sqlcipher: fix static linking

It uses openssl which for buildroot mandates libz, but doesn't link
against it so it fails. Fixes:
http://autobuild.buildroot.net/results/514/5145617f7c3cece933c845da3c9836d80d062bb6/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/sqlcipher/sqlcipher.mk

@@ -19,7 +19,7 @@ SQLCIPHER_CONF_OPT = \
 	--localstatedir=/var
 
 SQLCIPHER_CFLAGS += -DSQLITE_HAS_CODEC # Required according to the README
-SQLCIPHER_LDFLAGS += -lcrypto
+SQLCIPHER_LDFLAGS += -lcrypto -lz
 
 ifneq ($(BR2_LARGEFILE),y)
 # the sqlite configure script fails to define SQLITE_DISABLE_LFS when