meson: Replace obselete join_paths() with '/' operator

Since meson v0.49.0, join_paths() is equivalent to '/' hence,
drop and replace it with '/' short-hand in meson files.

This commit does not introduce any functional changes.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/raspberrypi/data/meson.build

@@ -10,4 +10,4 @@ conf_files = files([
 ])
 
 install_data(conf_files,
-             install_dir : join_paths(ipa_data_dir, 'raspberrypi'))
+             install_dir : ipa_data_dir / 'raspberrypi')