mm/init-mm.c: include <linux/mman.h> for vm_committed_as_batch

mm_init.c needs to include <linux/mman.h> for the definition of
vm_committed_as_batch.  Fixes the following sparse warning:

  mm/mm_init.c:141:5: warning: symbol 'vm_committed_as_batch' was not declared. Should it be static?

Link: http://lkml.kernel.org/r/20191016091509.26708-1-ben.dooks@codethink.co.uk
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/init-mm.c

@@ -5,6 +5,7 @@
 #include <linux/spinlock.h>
 #include <linux/list.h>
 #include <linux/cpumask.h>
+#include <linux/mman.h>
 
 #include <linux/atomic.h>
 #include <linux/user_namespace.h>