hwrng: drivers - Switch back to struct platform_driver::remove()

After commit 0edb555a ("platform: Make platform_driver::remove()
return void") .remove() is (again) the right callback to implement for
platform drivers.

Convert all platform drivers below drivers/char/hw_random to use
.remove(), with the eventual goal to drop struct
platform_driver::remove_new(). As .remove() and .remove_new() have the
same prototypes, conversion is done by just changing the structure
member name in the driver initializer.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>