lftp: fix static linking

Fixes http://autobuild.buildroot.net/results/14b/14b72a78936233b60dd893cef7803f909b846bea/

--with-modules only makes sense when linking shared, so disable when not.

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

package/lftp/lftp.mk

@@ -11,7 +11,9 @@ LFTP_LICENSE_FILES = COPYING
 LFTP_AUTORECONF = YES
 LFTP_DEPENDENCIES  = readline zlib
 
+ifneq ($(BR2_PREFER_STATIC_LIB),y)
 LFTP_CONF_OPT += --with-modules
+endif
 
 ifeq ($(BR2_PACKAGE_GNUTLS),y)
 LFTP_DEPENDENCIES += gnutls