"val" needs to be signed for the error handling to work.

Fixes: 6cd225cc ("hwrng: exynos - add Samsung Exynos True RNG driver")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NKrzysztof Kozlowski <krzk@kernel.org>
Acked-by: NŁukasz Stelmach <l.stelmach@samsung.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>