media: atomisp: Remove atomisp_mrfld_power_down()/_up()

atomisp_mrfld_power_down()/_up() are unnecessary wrappers around
atomisp_mrfld_power() remove them and just call atomisp_mrfld_power()
directly.

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