USB: gpio_vbus: handle IRQ flags properly

Currently, 'res->flags' handlings are wrong in three respects:
* the driver _modifies_ the contents of platform data
* res->flags is set up, but not used anywhere in the driver
* request_irq() always takes VBUS_IRQ_FLAGS, regardless of refs->flags

This patch tries to fix this with a policy: If a platform IRQ resource
is available, give preference to its IRQ flag(s) over a default one
(VBUS_IRQ_FLAGS).

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>