hwrng: ingenic - Fix a resource leak in an error handling path

In case of error, we should call 'clk_disable_unprepare()' to undo a
previous 'clk_prepare_enable()' call, as already done in the remove
function.

Fixes: 406346d2 ("hwrng: ingenic - Add hardware TRNG for Ingenic X1830")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Tested-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>