dm: core: Update uclass_find_next_free_req_seq() args

At present this is passed a uclass ID and it has to do a lookup. The
callers all have the uclass pointer, except for the I2C uclass where the
code will soon be deleted.

Update the argument to a uclass * instead of an ID since it is more
efficient.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/uclass-internal.h b/include/dm/uclass-internal.h
index 6e3f15c..2c21871 100644
--- a/include/dm/uclass-internal.h
+++ b/include/dm/uclass-internal.h
@@ -19,10 +19,10 @@
  * maximum req_seq of the uclass + 1.
  * This allows assiging req_seq number in the binding order.
  *
- * @id:		Id number of the uclass
+ * @uc:		uclass to check
  * @return	The next free req_seq number
  */
-int uclass_find_next_free_req_seq(enum uclass_id id);
+int uclass_find_next_free_req_seq(struct uclass *uc);
 
 /**
  * uclass_get_device_tail() - handle the end of a get_device call