bus/usb/ehci: Define GRUB_EHCI_TOGGLE as grub_uint32_t

bus/usb/ehci: Define GRUB_EHCI_TOGGLE as grub_uint32_t

The Coverity indicates that GRUB_EHCI_TOGGLE is an int that contains
a negative value and we are using it for the variable token which is
grub_uint32_t. To remedy this we can cast the definition to grub_uint32_t.

Fixes: CID 473851
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Gbp-Pq: Topic cve-2025-jan
Gbp-Pq: Name bus-usb-ehci-Define-GRUB_EHCI_TOGGLE-as-grub_uint32_t.patch