hwrng: omap3-rom - fix using wrong clk_disable() in omap_rom_rng_runtime_resume()

'ddata->clk' is enabled by clk_prepare_enable(), it should be disabled
by clk_disable_unprepare().

Fixes: 8d9d4bdc ("hwrng: omap3-rom - Use runtime PM instead of custom functions")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>