media: i2c: Remove .s_power() from ov7251

The .s_power() callback is deprecated, and now that we have pm_runtime
functionality in the driver there's no further use for it. Delete the
function.

Signed-off-by: Daniel Scally <djrscally@gmail.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>