omap-rng: fix use of SIMPLE_DEV_PM_OPS

omap_rng_suspend and omap_rng_resume are unused if CONFIG_PM is enabled
but CONFIG_PM_SLEEP is disabled. I found this while building all defconfig
files on ARM. It's not clear to me if this is the right solution, but
at least it makes the code consistent again.

Without this patch, building omap1_defconfig results in:

drivers/char/hw_random/omap-rng.c:165:12: warning: 'omap_rng_suspend' defined but not used [-Wunused-function]
drivers/char/hw_random/omap-rng.c:171:12: warning: 'omap_rng_resume' defined but not used [-Wunused-function]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kevin Hilman <khilman@ti.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Herbert Xu <herbert@gondor.apana.org.au>