Add 'const' keyword to chip write and other function prototypes

Corresponding to flashrom svn r1789.

Inspired by and mostly based on a patch
Signed-off-by: Mark Marshall <mark.marshall@omicron.at>

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/en29lv640b.c b/en29lv640b.c
index e79415a..110aa18 100644
--- a/en29lv640b.c
+++ b/en29lv640b.c
@@ -31,8 +31,7 @@
  */
 
 /* chunksize is 1 */
-int write_en29lv640b(struct flashctx *flash, uint8_t *src, unsigned int start,
-		     unsigned int len)
+int write_en29lv640b(struct flashctx *flash, const uint8_t *src, unsigned int start, unsigned int len)
 {
 	int i;
 	chipaddr bios = flash->virtual_memory;