bug.h: add include of it to various implicit C users

With bug.h currently living right in linux/kernel.h there
are files that use BUG_ON and friends but are not including
the header explicitly.  Fix them up so we can remove the
presence in kernel.h file.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/lib/plist.c b/lib/plist.c
index a0a4da4..6ab0e52 100644
--- a/lib/plist.c
+++ b/lib/plist.c
@@ -23,6 +23,7 @@
  * information.
  */
 
+#include <linux/bug.h>
 #include <linux/plist.h>
 #include <linux/spinlock.h>