V4L/DVB: v4l: radio: si470x: fix unneeded free_irq() call

In case of error during probe() the driver calls free_irq() function
on not yet allocated irq. This patches fixes the call sequence in case of
the error.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>