md: Add module.h to all files using it implicitly

A pending cleanup will mean that module.h won't be implicitly
everywhere anymore.  Make sure the modular drivers in md dir
are actually calling out for <module.h> explicitly in advance.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

drivers/md/linear.c

@@ -19,6 +19,7 @@
 #include <linux/blkdev.h>
 #include <linux/raid/md_u.h>
 #include <linux/seq_file.h>
+#include <linux/module.h>
 #include <linux/slab.h>
 #include "md.h"
 #include "linear.h"