block: constify sect_buf argument of ide_write_data

Add a const keyword to the sect_buf argument of
ide_write_data to fix the following warning:

  cmd_ide.c: In function '__ide_output_data':
  cmd_ide.c:548: warning: passing argument 2 of 'ide_write_data' discards qualifiers from pointer target type
  /devel/u-boot.git/include/ide.h:76: note: expected 'ulong *' but argument is of type 'const ulong *'

Also modify the driver-model documentation to
match with the new prototype.

Compile tested only.

Cc: Macpaul Lin <macpaul@andestech.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
diff --git a/doc/driver-model/UDM-block.txt b/doc/driver-model/UDM-block.txt
index 5d5c776..b42ec69 100644
--- a/doc/driver-model/UDM-block.txt
+++ b/doc/driver-model/UDM-block.txt
@@ -93,7 +93,7 @@
       uchar ide_read_register(int dev, unsigned int port);
       void  ide_write_register(int dev, unsigned int port, unsigned char val);
       void  ide_read_data(int dev, ulong *sect_buf, int words);
-      void  ide_write_data(int dev, ulong *sect_buf, int words);
+      void  ide_write_data(int dev, const ulong *sect_buf, int words);
 
     The first two functions are called from ide_inb()/ide_outb(), and will
     default to direct memory access if CONFIG_IDE_AHB is not set, or