media: atomisp: Remove struct atomisp_platform_data

media: atomisp: Remove struct atomisp_platform_data

struct atomisp_platform_data only has a single subdevs member. Remove
this struct and replace atomisp_get_platform_data() with
atomisp_platform_get_subdevs().

Note atomisp_get_platform_data() and now atomisp_platform_get_subdevs()
always succeed, so while at it also remove unnecessary error checking.

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