Fix kernel buuild with (CONFIG_COMPAT && ! CONFIG_BLOCK)

Commit 02a5e0acb3cb85d80d0fe834e366d38a92bbaa22 ("BLOCK: Hide the
contents of linux/bio.h if CONFIG_BLOCK=n") broke the kernel build for
the CONFIG_COMPAT && !CONFIG_BLOCK case:

    CC      fs/compat_ioctl.o
  In file included from include/linux/raid/md_k.h:19,
                   from include/linux/raid/md.h:54,
                   from fs/compat_ioctl.c:25:
  include/linux/raid/../../../drivers/md/dm-bio-list.h: In bio_list_:
  include/linux/raid/../../../drivers/md/dm-bio-list.h:40: error: dereferencing pointer to incomplete type
  include/linux/raid/../../../drivers/md/dm-bio-list.h: In bio_list_:
  include/linux/raid/../../../drivers/md/dm-bio-list.h:48: error: dereferencing pointer to incomplete type
  include/linux/raid/../../../drivers/md/dm-bio-list.h:51: error: dereferencing pointer to incomplete type
  include/linux/raid/../../../drivers/md/dm-bio-list.h: In bio_list_:
  include/linux/raid/../../../drivers/md/dm-bio-list.h:64: error: dereferencing pointer to incomplete type
  include/linux/raid/../../../drivers/md/dm-bio-list.h: In bio_list_merge_:
  include/linux/raid/../../../drivers/md/dm-bio-list.h:78: error: dereferencing pointer to incomplete type
  include/linux/raid/../../../drivers/md/dm-bio-list.h: In bio_list_:
  include/linux/raid/../../../drivers/md/dm-bio-list.h:90: error: dereferencing pointer to incomplete type
  include/linux/raid/../../../drivers/md/dm-bio-list.h:94: error: dereferencing pointer to incomplete type
  make[1]: *** [fs/compat_ioctl.o] Error 1
  make: *** [fs] Error 2

Signed-off-by: Andreas Herrmann <aherrman@arcor.de>
Acked-By: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/dm-bio-list.h

@@ -9,6 +9,8 @@
 
 #include <linux/bio.h>
 
+#ifdef CONFIG_BLOCK
+
 struct bio_list {
 	struct bio *head;
 	struct bio *tail;
@@ -106,4 +108,5 @@ static inline struct bio *bio_list_get(struct bio_list *bl)
 	return bio;
 }
 
+#endif /* CONFIG_BLOCK */
 #endif