catkin: improve formatting

During some code inspections, I discovered that two consecutive
empty lines slipped in with the commit 18588242.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@oss.bmw-carit.de>

recipes-ros/catkin/catkin_0.5.90.bb

 require catkin.inc
 
-
 DEPENDS_virtclass-native += "catkin-runtime"
 
 RDEPENDS_${PN}_class-native = ""