iwlwifi: bump FW API to 56 for AX devices

Start supporting API version 56 for AX devices.
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200529092401.aabbc5b472ee.I88cb2c3d2d07e62eac3671335ff1fb80b73c5839@changeid

drivers/net/wireless/intel/iwlwifi/cfg/22000.c

@@ -57,7 +57,7 @@
 #include "iwl-prph.h"
 
 /* Highest firmware API version supported */
-#define IWL_22000_UCODE_API_MAX	55
+#define IWL_22000_UCODE_API_MAX	56
 
 /* Lowest firmware API version supported */
 #define IWL_22000_UCODE_API_MIN	39