hwrng: npcm - use pm_runtime_resume_and_get() in npcm_rng_read()

npcm_rng_read() calls pm_runtime_get_sync() without checking the return value and then polls and reads the RNG registers: when resuming the device fails (negative return), the loop reads a device that never resumed and the failure is lost - the function returns the (zero) byte count instead of an error.

Use pm_runtime_resume_and_get() instead and bail out on the error: the helper reports the resume failure and drops the usage counter reference it took, which a failed pm_runtime_get_sync() leaves behind (the usage counter is incremented before the resume attempt, so returning directly after a failed get_sync() would leak the reference and the device could never autosuspend again). The tail pm_runtime_put_sync_autosuspend() must not be used for this bailout:
the device never resumed, so balancing the counter is all that is needed. On success the helper returns 0, which is exactly what the read counter expects at that point.

---
 drivers/char/hw_random/npcm-rng.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index a85f745963be..67a35df3bf80 100644
@@ -58,7 +58,9 @@ static int npcm_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 	int retval = 0;
 	int ready;
 
-	pm_runtime_get_sync(priv->dev);
+	retval = pm_runtime_resume_and_get(priv->dev);
+	if (retval < 0)
+		return retval;
 
 	while (max) {
 		if (wait) {

2.50.1.windows.1