usb: ucsi: stm32: Use min() to improve ucsi_stm32g0_fw_cb()

Use min() to improve ucsi_stm32g0_fw_cb() and avoid calculating
'end - data' twice.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20250830110426.10007-2-thorsten.blum@linux.dev


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>