crush: include header for global symbols

Include the header to pickup the definitions of the global symbols.

Quiets the following sparse warnings:

warning: symbol 'crush_find_rule' was not declared. Should it be static?
warning: symbol 'crush_do_rule' was not declared. Should it be static?
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Sage Weil <sage@newdream.net>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ceph/crush/mapper.c

@@ -20,6 +20,7 @@
 
 #include <linux/crush/crush.h>
 #include <linux/crush/hash.h>
+#include <linux/crush/mapper.h>
 
 /*
  * Implement the core CRUSH mapping algorithm.