drm/bridge: tpd12s015: Fix irq registering in tpd12s015_probe

gpiod_to_irq() return negative value in case of error,
the existing code doesn't handle negative error codes.
If the HPD gpio supports IRQs (gpiod_to_irq returns a
valid number), we use the IRQ. If it doesn't (gpiod_to_irq
returns an error), it gets polled via detect().

Fixes: cff5e6f7 ("drm/bridge: Add driver for the TI TPD12S015 HDMI level shifter")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201102143024.26216-1-yuehaibing@huawei.com