hwrng: exynos - use __maybe_unused to hide pm functions

The exynos random driver uses #ifdef to check for CONFIG_PM, but
then uses SIMPLE_DEV_PM_OPS, which leaves the references out when
CONFIG_PM_SLEEP is not defined, so we get a warning with
PM=y && PM_SLEEP=n:

drivers/char/hw_random/exynos-rng.c:166:12: error: 'exynos_rng_suspend' defined but not used [-Werror=unused-function]
drivers/char/hw_random/exynos-rng.c:171:12: error: 'exynos_rng_resume' defined but not used [-Werror=unused-function]

This removes the incorrect #ifdef and instead uses a __maybe_unused
annotation to let the compiler know it can silently drop
the function definition.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>