iio: pressure: bmp280: Fix NULL pointer exception

The bmp085 EOC IRQ support is optional, but the driver's common probe
function queries the IRQ properties whether or not it exists, which
can trigger a NULL pointer exception. Avoid any exception by making
the query conditional on the possession of a valid IRQ.

Fixes: aae95394

 ("iio: pressure: bmp280: add support for BMP085 EOC interrupt")
Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230811155829.51208-1-phil@raspberrypi.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>