fpga: constify to fix build warning

Fix compiler warning:

cmd_fpga.c:318: warning: passing argument 3 of 'fit_image_get_data'
from incompatible pointer type

Adding the needed 'const' here entails a whole bunch of additonal
changes all over the FPGA code.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Andre Schwarz <andre.schwarz@matrix-vision.de>
Cc: Murray Jensen <Murray.Jensen@csiro.au>
Acked-by: Andre Schwarz<andre.schwarz@matrix-vision.de>
diff --git a/include/altera.h b/include/altera.h
index f28a6a8..7a2bece 100644
--- a/include/altera.h
+++ b/include/altera.h
@@ -76,9 +76,9 @@
 
 /* Generic Altera Functions
  *********************************************************************/
-extern int altera_load( Altera_desc *desc, void *image, size_t size );
-extern int altera_dump( Altera_desc *desc, void *buf, size_t bsize );
-extern int altera_info( Altera_desc *desc );
+extern int altera_load(Altera_desc *desc, const void *image, size_t size);
+extern int altera_dump(Altera_desc *desc, const void *buf, size_t bsize);
+extern int altera_info(Altera_desc *desc);
 
 /* Board specific implementation specific function types
  *********************************************************************/
@@ -88,7 +88,7 @@
 typedef int (*Altera_done_fn)( int cookie );
 typedef int (*Altera_clk_fn)( int assert_clk, int flush, int cookie );
 typedef int (*Altera_data_fn)( int assert_data, int flush, int cookie );
-typedef int (*Altera_write_fn)(void *buf, size_t len, int flush, int cookie);
+typedef int(*Altera_write_fn)(const void *buf, size_t len, int flush, int cookie);
 typedef int (*Altera_abort_fn)( int cookie );
 typedef int (*Altera_post_fn)( int cookie );