pnp_device: improve readability

Add comments on the ops handling in pnp_enable_devices function and the
pnp_info struct.

Also remove the negation in the check if an LDN-specific override is used.
This patch doesn't change the logic though.

Change-Id: I3e80dbce1f29ee3e95e3b1d71c9b8479561d5c1a
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/27384
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
diff --git a/src/device/pnp_device.c b/src/device/pnp_device.c
index ba05c82..5600231 100644
--- a/src/device/pnp_device.c
+++ b/src/device/pnp_device.c
@@ -386,10 +386,13 @@
 		if (dev->ops)
 			continue;
 
-		if (info[i].ops == 0)
-			dev->ops = ops;
-		else
+		/* use LDN-specific ops override from corresponding pnp_info
+		   entry if not NULL */
+		if (info[i].ops)
 			dev->ops = info[i].ops;
+		/* else use device ops  */
+		else
+			dev->ops = ops;
 
 		get_resources(dev, &info[i]);
 	}