macb: fix build warning for !CONFIG_OF

When CONFIG_OF is disabled, we get a harmless warning about the
newly added variable:

drivers/net/ethernet/cadence/macb_main.c:48:39: error: 'mgmt' defined but not used [-Werror=unused-variable]
 static struct sifive_fu540_macb_mgmt *mgmt;

Move the variable closer to its use inside of the #ifdef.

Fixes: c218ad55 ("macb: Add support for SiFive FU540-C000")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb_main.c

@@ -45,8 +45,6 @@ struct sifive_fu540_macb_mgmt {
 	struct clk_hw hw;
 };
 
-static struct sifive_fu540_macb_mgmt *mgmt;
-
 #define MACB_RX_BUFFER_SIZE	128
 #define RX_BUFFER_MULTIPLE	64  /* bytes */
 
@@ -3628,6 +3626,8 @@ static int macb_init(struct platform_device *pdev)
 /* max number of receive buffers */
 #define AT91ETHER_MAX_RX_DESCR	9
 
+static struct sifive_fu540_macb_mgmt *mgmt;
+
 /* Initialize and start the Receiver and Transmit subsystems */
 static int at91ether_start(struct net_device *dev)
 {