usb: uhci-grlib: Explicitly include linux/platform_device.h

This fixes relying upon linux/of_platform.h to include
linux/platform_device.h, which it no longer does, thereby fixing
compilation problems like:

In file included from drivers/usb/host/uhci-hcd.c:850:
drivers/usb/host/uhci-grlib.c: In function 'uhci_hcd_grlib_probe':
drivers/usb/host/uhci-grlib.c:92:29: error: invalid use of undefined type 'struct platform_device'
   92 |  struct device_node *dn = op->dev.of_node;
      |                             ^~

Fixes: ef175b29

 ("of: Stop circularly including of_device.h and of_platform.h")
Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20240129075056.1511630-1-andreas@gaisler.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>