media: atomisp: fix inverted logic in buffers_needed()

When config.mode is IA_CSS_INPUT_MODE_BUFFERED_SENSOR, it rather needs
buffers. Fix it by inverting the return value.

Fixes: 3c0538fb ("media: atomisp: get rid of most checks for ISP2401 version")
Signed-off-by: Tsuchiya Yuto <kitakar@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>