iwlwifi: Legacy isr only used by legacy devices

Move iwl_isr_legacy function to iwl_legacy.c since it only used
by legacy devices.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-3945.c b/drivers/net/wireless/iwlwifi/iwl-3945.c
index d9e6764..a97c099 100644
--- a/drivers/net/wireless/iwlwifi/iwl-3945.c
+++ b/drivers/net/wireless/iwlwifi/iwl-3945.c
@@ -51,6 +51,7 @@
 #include "iwl-led.h"
 #include "iwl-3945-led.h"
 #include "iwl-3945-debugfs.h"
+#include "iwl-legacy.h"
 
 #define IWL_DECLARE_RATE_INFO(r, ip, in, rp, rn, pp, np)    \
 	[IWL_RATE_##r##M_INDEX] = { IWL_RATE_##r##M_PLCP,   \