dvb-apps: fix static linking with libiconv

Fixes http://autobuild.buildroot.net/results/4b5/4b56b89dd0ccd3b7e4017782e8d48b9c71207ff7/



Pass the libraries to be linked in LDLIBS instead of LDFLAGS so the end up
after the object files on the linker command line.

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