regmap: Fix return code for stub regmap_get_device()

We return a pointer, not an int.

Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index cd480fd..c5ed83f 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -733,7 +733,7 @@
 static inline struct device *regmap_get_device(struct regmap *map)
 {
 	WARN_ONCE(1, "regmap API is disabled");
-	return -EINVAL;
+	return NULL;
 }
 
 #endif