dump1090: fix librtlsdr package name typo
Fixes:
http://autobuild.buildroot.net/results/720/720a4b23a47aa6677bde4418f21e6b073a72ea51/
http://autobuild.buildroot.net/results/14e/14edf051d113a6ec54b61738748764adeac7ba9d/
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>