media: atomisp: Drop unnecessary first_streamoff check

Drop an unnecessary first_streamoff check from atomisp_streamoff(),
above the check there is a:

	if (!first_streamoff)
		goto stop_sensor;

Code block which will jump over the code with the test, so the test
is only executed when first_streamoff is true and therefor the test
is not necessary.

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