media: atomisp: Register /dev/* nodes at the end of atomisp_pci_probe()

Register /dev/* nodes at the end of atomisp_pci_probe(), this is
a prerequisite for dropping the loading mutex + ready flag kludge
for delaying open() calls on the /dev/* nodes .

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>