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/dummyflasher.c b/dummyflasher.c
index 2d7fa85..b9f6126 100644
--- a/dummyflasher.c
+++ b/dummyflasher.c
@@ -387,7 +387,7 @@
 	if (!stat(emu_persistent_image, &image_stat)) {
 		msg_pdbg("Found persistent image %s, %jd B ",
 			 emu_persistent_image, (intmax_t)image_stat.st_size);
-		if (image_stat.st_size == emu_chip_size) {
+		if ((uintmax_t)image_stat.st_size == emu_chip_size) {
 			msg_pdbg("matches.\n");
 			msg_pdbg("Reading %s\n", emu_persistent_image);
 			if (read_buf_from_file(flashchip_contents, emu_chip_size,