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: 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>