lib/dma-debug.c: fix __hash_bucket_find()

If there is only one match, the unique matched entry should be returned.

Without the fix, the upcoming dma debug interfaces ("dma-debug: new
interfaces to debug dma mapping errors") can't work reliably because
only device and dma_addr are passed to dma_mapping_error().

Signed-off-by: Ming Lei <[email protected]>
Reported-by: Wu Fengguang <[email protected]>
Cc: Joerg Roedel <[email protected]>
Tested-by: Shuah Khan <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

lib/dma-debug.c

@@ -264,7 +264,7 @@ static struct dma_debug_entry *__hash_bucket_find(struct hash_bucket *bucket,
 						  match_fn match)
 {
 	struct dma_debug_entry *entry, *ret = NULL;
-	int matches = 0, match_lvl, last_lvl = 0;
+	int matches = 0, match_lvl, last_lvl = -1;
 
 	list_for_each_entry(entry, &bucket->list, list) {
 		if (!match(ref, entry))
@@ -293,7 +293,7 @@ static struct dma_debug_entry *__hash_bucket_find(struct hash_bucket *bucket,
 		} else if (match_lvl > last_lvl) {
 			/*
 			 * We found an entry that fits better then the
-			 * previous one
+			 * previous one or it is the 1st match.
 			 */
 			last_lvl = match_lvl;
 			ret      = entry;