regmap: Ensure rbtree syncs registers set to zero properly

Simplify the check for registers set at their default value by avoiding
picking a default value in the case where we don't have one. Instead we
only compare the current value to the current value when we looked one
up. This fixes the case where we don't have a default stored but the value
was set to zero when that isn't the chip default.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>

drivers/base/regmap/regcache-rbtree.c

@@ -304,7 +304,7 @@ static int regcache_rbtree_sync(struct regmap *map)
 	struct rb_node *node;
 	struct regcache_rbtree_node *rbnode;
 	unsigned int regtmp;
-	unsigned int val, def;
+	unsigned int val;
 	int ret;
 	int i;
 
@@ -315,13 +315,12 @@ static int regcache_rbtree_sync(struct regmap *map)
 			regtmp = rbnode->base_reg + i;
 			val = regcache_rbtree_get_register(rbnode, i,
 							   map->cache_word_size);
+
+			/* Is this the hardware default?  If so skip. */
 			ret = regcache_lookup_reg(map, i);
-			if (ret < 0)
-				def = 0;
-			else
-				def = map->reg_defaults[ret].def;
-			if (val == def)
+			if (ret > 0 && val == map->reg_defaults[ret].def)
 				continue;
+
 			map->cache_bypass = 1;
 			ret = _regmap_write(map, regtmp, val);
 			map->cache_bypass = 0;