hwrng: stm32 - use pm_runtime_resume_and_get()

include/linux/pm_runtime.h pm_runtime_get_sync() description suggests to
... consider using pm_runtime_resume_and_get() instead of it, especially
if its return value is checked by the caller, as this is likely to result
in cleaner code.

This is indeed better, switch to pm_runtime_resume_and_get() which
correctly suspends the device again in case of failure. Also add error
checking into the RNG driver in case pm_runtime_resume_and_get() does
fail, which is currently not done, and it does detect sporadic -EACCES
error return after resume, which would otherwise lead to a hang due to
register access on un-resumed hardware. Now the read simply errors out
and the system does not hang.

Acked-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/stm32-rng.c

@@ -187,7 +187,9 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 	int retval = 0, err = 0;
 	u32 sr;
 
-	pm_runtime_get_sync((struct device *) priv->rng.priv);
+	retval = pm_runtime_resume_and_get((struct device *)priv->rng.priv);
+	if (retval)
+		return retval;
 
 	if (readl_relaxed(priv->base + RNG_SR) & RNG_SR_SEIS)
 		stm32_rng_conceal_seed_error(rng);