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/fpga.h b/include/fpga.h
index ac24f2b..e0b1fe7 100644
--- a/include/fpga.h
+++ b/include/fpga.h
@@ -72,11 +72,11 @@
 
 
 /* root function definitions */
-extern void fpga_init( void );
-extern int fpga_add( fpga_type devtype, void *desc );
-extern int fpga_count( void );
-extern int fpga_load( int devnum, void *buf, size_t bsize );
-extern int fpga_dump( int devnum, void *buf, size_t bsize );
-extern int fpga_info( int devnum );
+extern void fpga_init(void);
+extern int fpga_add(fpga_type devtype, void *desc);
+extern int fpga_count(void);
+extern int fpga_load(int devnum, const void *buf, size_t bsize);
+extern int fpga_dump(int devnum, const void *buf, size_t bsize);
+extern int fpga_info(int devnum);
 
 #endif	/* _FPGA_H_ */