Fix more sign-compare issues

The one in the `dummyflasher` is a little peculiar. We actually never
knew the type of the `st_size` field in `struct stat`. It happens to
be `signed` in some systems (e.g. DJGPP).

Change-Id: If36ba22606021400b385ea6083eacc7b360c20c5
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/35800
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/dediprog.c b/dediprog.c
index fbd6930..e4124b0 100644
--- a/dediprog.c
+++ b/dediprog.c
@@ -1038,7 +1038,7 @@
 			free(device);
 			return 1;
 		}
-		if (usedevice < 0 || usedevice > UINT_MAX) {
+		if (usedevice < 0 || usedevice > INT_MAX) {
 			msg_perr("Error: Value for 'device' is out of range.\n");
 			free(device);
 			return 1;