cmake: Fix pkg-config file

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

libssh.pc.cmake

@@ -1,6 +1,6 @@
-Name: ${APPLICATION_NAME}
+Name: ${PROJECT_NAME}
 Description: The SSH Library
-Version: ${APPLICATION_VERSION}
+Version: ${PROJECT_VERSION}
 Libs: -L${LIB_INSTALL_DIR} -lssh
 Cflags: -I${INCLUDE_INSTALL_DIR}