drivers: usb_dc_rpi_pico: previosuly used endpoint may remain locked

When reconfiguring a previously used endpoint, it may still be locked
when a write was taking place when e.g. the host application crashed.
The call to udc_rpi_cancel_endpoint seems to do a proper cleanup of
the endpoint, i.e. the write semaphore will be released.
Fixes #66723.

Signed-off-by: Manuel Aebischer <manuel.aebischer@netmodule.com>