vlc: fix svg support

In vlc, svg support is done using librsvg, not libsvg.

Fixes:
  http://autobuild.buildroot.org/results/344/344af6e756a5f2c1ee515a355ae5b288401c4c71/build-end.log
  http://autobuild.buildroot.org/results/19f/19f1450ed5453aa666bc7aae2e965ad81e5f845d/build-end.log



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>