media: atomisp: Fix double negation in unsupported revision error

s/is not unsupported/is not supported/ in the unsupported revision
error.

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