iwlwifi: fix iwl-rx.c compilation

My commit 466a19a0 "iwlwifi: move rx
handlers code to iwl-rx.c" breaks compilation on 32 bits. Fix that.
Reported-by: NGuy, Wey-Yi <wey-yi.w.guy@intel.com>
Reported-by: NDaniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: NStanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: NJohn 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"