Fix incorrect check for LOG_UEVENTS

LOG_UEVENTS is a boolean value as defined in system/core/init/init.h.
Therefore, code should use an #if check and not an #ifdef check as the
macro will always be defined.
diff --git a/init/devices.c b/init/devices.c
index 60f9b9c..606a074 100644
--- a/init/devices.c
+++ b/init/devices.c
@@ -288,7 +288,7 @@
     chown(path, uid, gid);
 }
 
-#ifdef LOG_UEVENTS
+#if LOG_UEVENTS
 
 static inline suseconds_t get_usecs(void)
 {