V4L/DVB (8039): pxa-camera: fix platform_get_irq() error handling.

platform_get_irq() returns a negative value on error, not 0.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>