README: Fix typo in description of CONFIG_OF_EMBED

The correct name is 'gd->fdt_blob', not 'gd->blob'.
Signed-off-by: NNobuhiro Iwamatsu <iwamatsu@nigauri.org>
CC: Simon Glass <sjg@chromium.org>
Reviewed-by: NSimon Glass <sjg@chromium.org>

README

@@ -776,7 +776,7 @@ The following options need to be configured:
 		binary in its image. This device tree file should be in the
 		board directory and called <soc>-<board>.dts. The binary file
 		is then picked up in board_init_f() and made available through
-		the global data structure as gd->blob.
+		the global data structure as gd->fdt_blob.
 
 		CONFIG_OF_SEPARATE
 		If this variable is defined, U-Boot will build a device tree