hwrng: pic32 - use devm_clk_get_enabled

Use devm_clk_get_enabled in the pic32 driver. Ensure that the clock is
enabled as long as the driver is registered with the hwrng core.

Fixes: 7ea39973 ("hwrng: pic32 - Use device-managed registration API")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>