crypto: sahara - propagate the error on clk_disable_unprepare() failure

clk_prepare_enable() may fail, so we should better check its return value
and propagate it in the case of error.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>