drivers/net/enic: fix sparse warning: make symbol static

Fix this sparse warning:

  drivers/net/enic/vnic_dev.c:288:5: warning: symbol 'vnic_dev_capable' was not declared. Should it be static?
Signed-off-by: NHannes Eder <hannes@hanneseder.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/enic/vnic_dev.c

@@ -285,7 +285,7 @@ int vnic_dev_cmd(struct vnic_dev *vdev, enum vnic_devcmd_cmd cmd,
 	return -ETIMEDOUT;
 }
 
-int vnic_dev_capable(struct vnic_dev *vdev, enum vnic_devcmd_cmd cmd)
+static int vnic_dev_capable(struct vnic_dev *vdev, enum vnic_devcmd_cmd cmd)
 {
 	u64 a0 = (u32)cmd, a1 = 0;
 	int wait = 1000;