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/programmer.h b/programmer.h
index f4e8b46..dfa6ebd 100644
--- a/programmer.h
+++ b/programmer.h
@@ -304,7 +304,7 @@
 
 /* cbtable.c */
 int cb_parse_table(const char **vendor, const char **model);
-int cb_check_image(const uint8_t *bios, int size);
+int cb_check_image(const uint8_t *bios, unsigned int size);
 
 /* dmi.c */
 #if defined(__i386__) || defined(__x86_64__)