uboot-imx

cmd: usb: check if_type before using this device

For legacy usb storage driver, USB_MAX_STOR_DEV is defined as 7.
If we only have one usb disk on board, `usb dev 0` is ok.
But if `usb dev 1`, still ok, then `usb read xxx` will trigger
system fault and reboot.

So check if_type before using this device.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stephen Warren <swarren@nvidia.com>