crypto: atmel-sha204a - Use device-managed registration API

Use devm_hwrng_register to get rid of manual
unregistration.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>