firewire: cdev: address handler input validation

Like before my commit 1415d9189e8c59aa9c77a3bba419dcea062c145f,
fw_core_add_address_handler() does not align the address region now.
Instead the caller is required to pass valid parameters.

Since one of the callers of fw_core_add_address_handler() is the cdev
userspace interface, we now check for valid input.  If the client is
buggy, we give it a hint with -EINVAL.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/fw-cdev.c b/drivers/firewire/fw-cdev.c
index 094aee5..44af452 100644
--- a/drivers/firewire/fw-cdev.c
+++ b/drivers/firewire/fw-cdev.c
@@ -591,9 +591,10 @@
 	handler->closure = request->closure;
 	handler->client = client;
 
-	if (fw_core_add_address_handler(&handler->handler, &region) < 0) {
+	ret = fw_core_add_address_handler(&handler->handler, &region);
+	if (ret < 0) {
 		kfree(handler);
-		return -EBUSY;
+		return ret;
 	}
 
 	handler->resource.release = release_address_handler;