fix gcc warnings about uninitialized variables

like:

src/shared/install.c: In function ‘unit_file_lookup_state’:
src/shared/install.c:1861:16: warning: ‘r’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
         return r < 0 ? r : state;
                ^
src/shared/install.c:1796:13: note: ‘r’ was declared here
         int r;
             ^

1 files changed, 1 insertions, 1 deletions

diff --git a/src/udev/net/link-config.c b/src/udev/net/link-config.c
index 361de0d18..86d09bbff 100644
--- a/src/udev/net/link-config.c
+++ b/src/udev/net/link-config.c
@@ -469,7 +469,7 @@ int link_config_apply(link_config_ctx *ctx, link_config *config,
 
 int link_get_driver(link_config_ctx *ctx, struct udev_device *device, char **ret) {
         const char *name;
-        char *driver;
+        char *driver = NULL;
         int r;
 
         name = udev_device_get_sysname(device);