media: atomisp: only initialize mode if pipe is not null

During atomisp register, udev tries to open all devices. For
some, pipe is NULL, at least during register time, causing the
driver to try to access a NULL pointer.

So, add an extra check to avoid such condition.

Link: https://lore.kernel.org/linux-media/6406265f2d5f3791d5c7cbd1364186217f19524c.1636364423.git.mchehab+huawei@kernel.org


Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>