kernel: owl-loader: fix compile warning

check if the config option CONFIG_LANTIQ is defined.
This fixes the following warning:
  CC [M]  drivers/misc/owl-loader.o
drivers/misc/owl-loader.c: In function 'ath9k_pci_fixup':
drivers/misc/owl-loader.c:92:5: warning: "CONFIG_LANTIQ" is not defined [-Wundef]
 #if CONFIG_LANTIQ
     ^

Fixes: e9401a2335 ("kernel: owl-loader for delayed Atheros ath9k fixup")
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/generic/files/drivers/misc/owl-loader.c

@@ -89,7 +89,7 @@ static int ath9k_pci_fixup(struct pci_dev *pdev, const u16 *cal_data,
 			val = swahb32(val);
 		}
 
-#if CONFIG_LANTIQ
+#ifdef CONFIG_LANTIQ
 		val = swab32(val);
 #endif