bcache: Add missing #include <linux/prefetch.h>

m68k/allmodconfig:

drivers/md/bcache/bset.c: In function ‘bset_search_tree’:
drivers/md/bcache/bset.c:727: error: implicit declaration of function ‘prefetch’

drivers/md/bcache/btree.c: In function ‘bch_btree_node_get’:
drivers/md/bcache/btree.c:933: error: implicit declaration of function ‘prefetch’

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Kent Overstreet <koverstreet@google.com>

drivers/md/bcache/bset.c

@@ -10,6 +10,7 @@
 #include "debug.h"
 
 #include <linux/random.h>
+#include <linux/prefetch.h>
 
 /* Keylists */
 

drivers/md/bcache/btree.c

@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/bitops.h>
 #include <linux/hash.h>
+#include <linux/prefetch.h>
 #include <linux/random.h>
 #include <linux/rcupdate.h>
 #include <trace/events/bcache.h>