usb: gadget: udc: bcm63xx: Convert to use list_count_nodes()

The list API provides the list_count_nodes() to help with counting
existing nodes in the list. Utilise it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20221130134838.23805-3-andriy.shevchenko@linux.intel.com


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