media: atomisp: Remove res_overflow parameter from atomisp_try_fmt()

The only remaining caller of atomisp_try_fmt() always passes NULL
for the res_overflow parameter. Drop it and simplify atomisp_try_fmt().

Reviewed-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>