hamradio/yam: fix info leak in ioctl

The yam_ioctl() code fails to initialise the cmd field
of the struct yamdrv_ioctl_cfg. Add an explicit memset(0)
before filling the structure to avoid the 4-byte info leak.

Signed-off-by: Salva Peiró <speiro@ai2.upv.es>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int yam_info_open(struct inode *inode, struct file *file)
{
	return seq_open(file, &yam_seqops);
}

static int yam_info_open(struct inode *inode, struct file *file)
{
	return seq_open(file, &yam_seqops);
}
