iwlegacy: make array interval static, makes object smaller

Don't populate the array interval on the stack but instead make it
static. Makes the object code smaller by 121 bytes.

Before:
   text	   data	    bss	    dec	    hex	filename
 167797	  29676	    448	 197921	  30521	wireless/intel/iwlegacy/common.o

After:
   text	   data	    bss	    dec	    hex	filename
 167580	  29772	    448	 197800	  304a8	wireless/intel/iwlegacy/common.o

(gcc version 9.2.1, amd64)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/intel/iwlegacy/common.c

@@ -1072,7 +1072,7 @@ EXPORT_SYMBOL(il_get_channel_info);
 static void
 il_build_powertable_cmd(struct il_priv *il, struct il_powertable_cmd *cmd)
 {
-	const __le32 interval[3][IL_POWER_VEC_SIZE] = {
+	static const __le32 interval[3][IL_POWER_VEC_SIZE] = {
 		SLP_VEC(2, 2, 4, 6, 0xFF),
 		SLP_VEC(2, 4, 7, 10, 10),
 		SLP_VEC(4, 7, 10, 10, 0xFF)