media: atomisp-mt9m114: remove dead data

It seems that, originally, the logic would allow selecting between
fine and coarse integration. However, only coarse seems to be
implemented.

Get rid of this warning:

  drivers/staging/media/atomisp/i2c/atomisp-mt9m114.c: In function 'mt9m114_s_exposure':
  drivers/staging/media/atomisp/i2c/atomisp-mt9m114.c:1003:6: warning: variable 'exposure_local' set but not used [-Wunused-but-set-variable]
    u16 exposure_local[3];
        ^~~~~~~~~~~~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>