Fix -Wsign-compare trouble

Mostly by changing to `unsigned` types where applicable, sometimes
`signed` types, and casting as a last resort.

Change-Id: I08895543ffb7a48058bcf91ef6500ca113f2d305
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/30409
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jacob Garber <jgarber1@ualberta.ca>
diff --git a/it87spi.c b/it87spi.c
index f8b2b0f..f5955fe 100644
--- a/it87spi.c
+++ b/it87spi.c
@@ -281,7 +281,6 @@
 				    unsigned char *readarr)
 {
 	uint8_t busy, writeenc;
-	int i;
 
 	do {
 		busy = INB(it8716f_flashport) & 0x80;
@@ -330,6 +329,8 @@
 		| ((readcnt & 0x3) << 2) | (writeenc), it8716f_flashport);
 
 	if (readcnt > 0) {
+		unsigned int i;
+
 		do {
 			busy = INB(it8716f_flashport) & 0x80;
 		} while (busy);