docs: blockdev: add it to the admin-guide

The blockdev book basically contains user-faced documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 5c99e52..f652c1a 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -4424,7 +4424,7 @@ static int __init floppy_setup(char *str)
 		pr_cont("\n");
 	} else
 		DPRINT("botched floppy option\n");
-	DPRINT("Read Documentation/blockdev/floppy.rst\n");
+	DPRINT("Read Documentation/admin-guide/blockdev/floppy.rst\n");
 	return 0;
 }