mkimage: struct stat.st_size may not be long

The component st_size of struct stat is of type off_t. Depending on the
system printing it using %ld leads to a warning:

tools/mkimage.c:438:54: warning: format '%ld' expects argument of type
'long int', but argument 5 has type
'off_t' {aka 'long long int'} [-Wformat=]
  438 |     "%s: Bad size: \"%s\" is not valid image: size %ld < %u\n",
      |                                                    ~~^
      |                                                      |
      |                                                      long int
      |                                                    %lld

When comparing an off_t value to a 32bit integer we should not convert to
uint32_t but to off_t which may be wider.

Reported-by: Milan P. Stanić <mps@arvanta.net>
Fixes: 331f0800f1a3 ("mkimage: allow -l to work on block devices on Linux")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
diff --git a/tools/mkimage.c b/tools/mkimage.c
index ddb7933..0ec28da 100644
--- a/tools/mkimage.c
+++ b/tools/mkimage.c
@@ -435,11 +435,12 @@
 				params.cmdname, params.imagefile);
 			exit (EXIT_FAILURE);
 #endif
-		} else if ((unsigned)sbuf.st_size < tparams->header_size) {
+		} else if (sbuf.st_size < (off_t)tparams->header_size) {
 			fprintf (stderr,
-				"%s: Bad size: \"%s\" is not valid image: size %ld < %u\n",
+				"%s: Bad size: \"%s\" is not valid image: size %llu < %u\n",
 				params.cmdname, params.imagefile,
-				sbuf.st_size, tparams->header_size);
+				(unsigned long long) sbuf.st_size,
+				tparams->header_size);
 			exit (EXIT_FAILURE);
 		} else {
 			size = sbuf.st_size;