media: stm32-dcmi: fix irq = 0 case

Manage the irq = 0 case, where we shall return an error.

Fixes: b5b5a27b ("media: stm32-dcmi: return appropriate error codes during probe")

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Reported-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>