dm: blk: Fix warning on !CONFIG_BLK

When we don't have CONFIG_BLK defined we don't have a forward
declaration of struct udevice, and thus get a warning about it on
blk_get_from_parent(), which we only have when CONFIG_BLK is set.  Move
the declaration of blk_get_from_parent() to be with the other CONFIG_BLK
parts.

Fixes 9f103b9cb5 ("dm: blk: Add a way to obtain a block device from ...")
Signed-off-by: Tom Rini <trini@konsulko.com>

include/blk.h

@@ -377,6 +377,13 @@ int blk_find_max_devnum(enum if_type if_type);
  */
 int blk_select_hwpart(struct udevice *dev, int hwpart);
 
+/**
+ * blk_get_from_parent() - obtain a block device by looking up its parent
+ *
+ * All devices with
+ */
+int blk_get_from_parent(struct udevice *parent, struct udevice **devp);
+
 #else
 #include <errno.h>
 /*
@@ -616,11 +623,4 @@ ulong blk_write_devnum(enum if_type if_type, int devnum, lbaint_t start,
  */
 int blk_select_hwpart_devnum(enum if_type if_type, int devnum, int hwpart);
 
-/**
- * blk_get_from_parent() - obtain a block device by looking up its parent
- *
- * All devices with
- */
-int blk_get_from_parent(struct udevice *parent, struct udevice **devp);
-
 #endif