spl: fix format of function documentation

U-Boot adopted the kernel-doc annotation style.

cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/spl.h b/include/spl.h
index b31c9bb..580e4e0 100644
--- a/include/spl.h
+++ b/include/spl.h
@@ -155,7 +155,7 @@
 #endif
 };
 
-/*
+/**
  * Information required to load data from a device
  *
  * @dev: Pointer to the device, e.g. struct mmc *