Fix a trivial calloc warning

Change-Id: Id457c15555a6ca6333474601f92982446afa40ab
Signed-off-by: Richard Hughes <richard@hughsie.com>
Reviewed-on: https://review.coreboot.org/c/31223
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/flashrom.c b/flashrom.c
index cb2da46..e82c32e 100644
--- a/flashrom.c
+++ b/flashrom.c
@@ -1461,7 +1461,7 @@
 int read_flash_to_file(struct flashctx *flash, const char *filename)
 {
 	unsigned long size = flash->chip->total_size * 1024;
-	unsigned char *buf = calloc(size, sizeof(char));
+	unsigned char *buf = calloc(size, sizeof(unsigned char));
 	int ret = 0;
 
 	msg_cinfo("Reading flash... ");