media: atomisp: set DFS to MAX if sensor doesn't report fps

If the sensor doesn't implement support for g_frame_interval,
it won't return the expected fps rate.

Instead of keeping DFS on its minimal value (which will likely
not work), set it to the max.

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