iwlwifi: fix iwl-rx.c compilation

My commit 466a19a003f3b45a755bc85f967c21da947f9a00 "iwlwifi: move rx
handlers code to iwl-rx.c" breaks compilation on 32 bits. Fix that.

Reported-by: Guy, Wey-Yi <wey-yi.w.guy@intel.com>
Reported-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-rx.c

@@ -29,6 +29,7 @@
 
 #include <linux/etherdevice.h>
 #include <linux/slab.h>
+#include <linux/sched.h>
 #include <net/mac80211.h>
 #include <asm/unaligned.h>
 #include "iwl-eeprom.h"