wifi: ath9k: fix ath9k_use_msi declaration

Sparse warns:

drivers/net/wireless/ath/ath9k/init.c:79:5: warning: symbol 'ath9k_use_msi' was not declared. Should it be static?

Move the extern to ath9k.h so that it's visible in init.c.

Compile tested only.

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://msgid.link/20240320170656.3534265-3-kvalo@kernel.org

drivers/net/wireless/ath/ath9k/ath9k.h

@@ -39,6 +39,7 @@ extern int ath9k_modparam_nohwcrypt;
 extern int ath9k_led_blink;
 extern bool is_ath9k_unloaded;
 extern int ath9k_use_chanctx;
+extern int ath9k_use_msi;
 
 /*************************/
 /* Descriptor Management */

drivers/net/wireless/ath/ath9k/pci.c

@@ -21,8 +21,6 @@
 #include <linux/module.h>
 #include "ath9k.h"
 
-extern int ath9k_use_msi;
-
 static const struct pci_device_id ath_pci_id_table[] = {
 	{ PCI_VDEVICE(ATHEROS, 0x0023) }, /* PCI   */
 	{ PCI_VDEVICE(ATHEROS, 0x0024) }, /* PCI-E */