pkgconfig: vcsm: Add -lvcos to Libs

libvcsm.so is linked with vcos in
host_applications/linux/libs/sm/CMakeLists.txt , so changed to specify
it in pkgconfig file.

pkgconfig/vcsm.pc.in

@@ -6,5 +6,5 @@ includedir=${prefix}/include
 Name: VCSM
 Description: VideoCore Shared Memory library for RPi
 Version: 1
-Libs: -L${libdir} -lvcsm
+Libs: -L${libdir} -lvcsm -lvcos
 Cflags: -I${includedir}