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/programmer.c b/programmer.c
index bf7dca1..1874929 100644
--- a/programmer.c
+++ b/programmer.c
@@ -78,8 +78,7 @@
 	return val;
 }
 
-void fallback_chip_writen(const struct flashctx *flash, uint8_t *buf,
-			  chipaddr addr, size_t len)
+void fallback_chip_writen(const struct flashctx *flash, const uint8_t *buf, chipaddr addr, size_t len)
 {
 	size_t i;
 	for (i = 0; i < len; i++)