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/string.c b/lib/string.c
index dc4a863..0573a20 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -22,6 +22,7 @@
 #include <linux/types.h>
 #include <linux/string.h>
 #include <linux/ctype.h>
+#include <linux/bug.h>
 #include <linux/module.h>
 
 #ifndef __HAVE_ARCH_STRNICMP