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/drivers/fpga/altera.c b/drivers/fpga/altera.c
index 103d81c..f087d01 100644
--- a/drivers/fpga/altera.c
+++ b/drivers/fpga/altera.c
@@ -45,7 +45,7 @@
 static int altera_validate (Altera_desc * desc, const char *fn);
 
 /* ------------------------------------------------------------------------- */
-int altera_load( Altera_desc *desc, void *buf, size_t bsize )
+int altera_load(Altera_desc *desc, const void *buf, size_t bsize)
 {
 	int ret_val = FPGA_FAIL;	/* assume a failure */
 
@@ -85,7 +85,7 @@
 	return ret_val;
 }
 
-int altera_dump( Altera_desc *desc, void *buf, size_t bsize )
+int altera_dump(Altera_desc *desc, const void *buf, size_t bsize)
 {
 	int ret_val = FPGA_FAIL;	/* assume a failure */