usb: dwc3: Switch to platform_get_irq_byname_optional()

The dwc3 code to get the "peripheral" / "host" / "otg" IRQ first tries
platform_get_irq_byname() and then falls back to the IRQ at index 0 if
the platform_get_irq_byname().

In this case we do not want platform_get_irq_byname() to print an error
on failure, so switch to platform_get_irq_byname_optional() instead which
does not print an error.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=205037
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Link: https://lore.kernel.org/r/20191005210449.3926-3-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>