media: atomisp: Remove sw_contex.power_state checks

Remove the unnecessary sw_contex.power_state checks:

1. atomisp_freq_scaling() and atomisp_stop_streaming() only run when the
   ISP is powered up through runtime-pm, so the checks are not necessary

2. atomisp_mrfld_pre_power_down() and atomisp_runtime_resume() are only
   called through the driver-core pm handling code which already
   guarantees they are not called when already powered down / up.

3. atomisp_isr() also checks isp->css_initialized which only gets set
   by atomisp_css_init() which runs *after* powering up the ISP and which
   gets cleared by atomisp_css_uninit() *before* powering down the ISP.

So all the checks are unnecessary, remove them as well as the
sw_contex.power_state field itself.

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>